Columbia  ^nibergitp 
intfjeCitpofi^etoPorb  ^^^J] 

College  of  ^tjpsiciang  anb  burgeons 


^ 


Eeferente  Hibrarp 


T resented  hy 

^  DR.  WILLIAM  J.  GIES  J^' 

^o  enrich  the  library  resources 
available  to  holders 
'"^1  of  the 

GlES  FELLOWSHIP 

in  Biological  Chemistry 


'^^Cv-X 


LECTURE-NOTES 

ON 

CHEMISTRY 

FOR 

DENTAL    STUDENTS 


INCLUDING 

DENTAL    CHEMISTRY    OF    ALLOYS,    AMALGAMS,    ETC. 
SUCH     PORTIONS     OF      ORGANIC      AND      PHYSIOLOGICAL      CHEMISTRY     AS 

HAVE    PRACTICAL    BEARING    ON    THE    SUBJECT    OF    DENTISTRY 

AN     INORGANIC     QUALITATIVE      ANALYSIS     WITH     SPECIALLY     ADAPTED 

BLOWPIPE    AND    MICROSCOPICAL    TESTS,    AND    THE    CHEMICAL 

EXAMINATION    OF    URINE    AND    SALIVA 

BY 

H.   CARLTON   SMITH,  Ph.G. 

LECTUSER   ON  PHYSIOLOGICAL   AND   DENTAL   CHEMISTRY   AT    HARVARD    UNIVERSITY 

DENTAL    school;     HONORARY   MEMBER    OF   AMERICAN   ACADEMY    OF   DENTAL 

SCIENCE,    1906;    OF   THE    METROPOLITAN    SOCIETY    OF    MASSACHUSETTS 

STATE   DENTAL   ASSOCIATION,    I907;   OF   HARVARD   DENTAL 

ALUMNI,    I910;   AND   NORTHERN   OHIO   DENTAL 

ASSOCIATION,    191 2 

THIRD  EDITION  REVISED  AND  ENLARGED 
FIRST    THOUSAND 


NEW  YORK 
.     JOHN  WILEY  &   SONS,  Inc. 
London:   CHAPMAN  &  HALL,   Limited 
1917 


Copyright,  igo6,  1912,  1917, 

BY 

H.   CARLTON    SMITH 

r 


(t^n 


\ 


Stanbopc  iPress 

F.    H.  GILSON    COMPANY 
BOSTON,  U.S.A. 


PREFACE    TO    THIRD    EDITION 

Three  conditions  are  responsible  for  this  third  edition  of  a 
Dental  Chemistr}-:  first,  the  increasing  demand  for  more 
thorough  chemical  education  for  dental  students;  second,  the 
immense  amount  of  new  and  valuable  material  constantly- 
appearing  as  the  result  of  physiological  and  dental  research; 
and,  third,  the  apparent  demand  for  a  book  which  shall  be  of 
general  use  to  the  dental  profession  aside  from  its  usefulness  as 
a  classroom  textbook. 

In  the  effort  to  increase  the  working  value  of  the  book  some 
methods  and  many  references  have  been  included  which  would 
be  unnecessary  if  it  were  designed  for  school  use  only. 

To  facilitate  the  use  of  the  book  in  other  classes  than  my  own, 
experiments  have  been  grouped  at  the  end  in  the  beHef  that  a 
selection  may  be  more  easily  made  from  this  arrangement  than 
if  they  were  scattered  throughout  the  text. 

The  outHne  character  of  pre\'ious  editions  has  been  maintained 
and  the  student  is  expected  to  have  access  to  more  complete 
works,  such  as  those  included  in  the  following  list,  which  is 
•strongly  recommended  and  to  which  frequent  references  have 
been  made. 

QuaKtative  Analysis Stieglitz 

Qualitative  Analysis Prescott  and  Johnson 

Dental  ^letallurgy Hepburn  or  Essig 

Organic  Chemistry Norris 

Physiological  Chemistry.  . Hawk,  Fifth  Edition 

IMetaboUsm Tibbies 

References  have  also  been  made  to  current  dental  Htera- 
ture,  not  to  bring  the  book  strictly  up  to  date,  which  is  practi- 
cally impossible,  but  rather  to  teach  the  student  how  to  study, 
which  is  a  more  important  object  of  any  course  than  mere 
famUiaritv  with  present  day  theories. 

H.  C.  S. 

iii 


Digitized  by  tine  Internet  Arciiive 

in  2010  witii  funding  from 

Open  Knowledge  Commons 


http://www.archive.org/details/lecturenotesonch1917smit 


TO    THE    STUDENT 

As  the  student  of  dentistry  takes  up  the  study  of  chemistry, 
it  is  necessary  that  he  should  reahze  that  the  course  will  be  of 
value  to  him  in  the  ability  acquired  to  draw  correct  inferences 
from  observed  phenomena,  and  in  the  attainment  of  accuracy 
and  delicacy  in  manipulation,  fully  as  much  as  in  amount  of 
chemical  knowledge  obtained.  In  other  words,  he  must  do  his 
own  thinking,  carry  out  his  own  processes  and  experiments,  make 
his  own  analyses,  or  the  time  spent  will  be  little  better  than 
wasted,  for  the  chemical  facts  which  he  may  happen  to  remem- 
ber will  be  of  slight  benefit  in  the  work  to  which  every  student, 
worthy  of  the  name,  aspires,  that  of  developing,  broadening  and 
elevating  the  profession  which  he  has  chosen  as  his  own. 

The  course  of  study  outlined  in  this  book  is  designed  to 
furnish  the  starting-points,  which  will  be  of  practical  value  in 
solving  the  problems  constantly  presenting  themselves  for  con- 
sideration in  the  various  branches  of  chemistry.  It  is  hoped 
that  these  starting-points  may,  in  the  future,  serve  as  the  basis 
for  work  along  the  lines  of  original  research  and  that  the  best 
interests  of  dental  science  may  be  furthered  thereby. 

It  is  supposed  that  the  student  has  had  the  advantage  of  a 
laboratory  training  in  general  chemistry  and  is  conversant 
with  the  properties  and  methods  of  preparation  of  the  so-called 
non-metallic  elements,  also  with  the  fundamental  principles 
and  laws  of  theoretical  and  physical  chemistry;  that  he  is 
familiar  with  laboratory  apparatus,  such  as  test-tubes,  beakers, 
crucibles,  casseroles,  evapora ting-dishes,  retorts,  etc.,  and  that 
he  has  had  some  experience  in  the  ordinary  processes  of  pre- 
cipitation, filtration,  evaporation,  distillation,  subHmation,  and 
crystallization. 


vi  TO   THE  STUDENT 

If  there  is  any  feeling  of  insufficient  preparation  it  is  strongly 
advised  that  a  short  course  of  preliminary  study  be  taken. 
Chemistry  furnishes  the  groundwork  of  all  branches  of  medical 
science  to  a  much  greater  extent  than  we  are  apt  to  think, 
and  even  in  the  study  of  subjects  which  in  times  past  have 
been  carried  on  with  little  reference  to  chemistry,  we  now  see 
the  desirability  if  not  the  necessity  of  a  good  general  knowl- 
edge of  chemical  science.  The  physiologist  and  the  bacteriolo- 
gist are  to-day  turning  to  chemistry  for  the  ultimate  solution 
of  their  most  perplexing  problems. 

H.  C.  S. 


DIRECTIONS   FOR   STUDY* 

These  points  carefully  followed  will  enable  you  to  get  your 
lessons  more  easily,  more  quickly  and  to  remember  them  longer 
than  you  otherwise  would. 

(i)  Let  your  lecture  notes  consist  of  a  very  complete,  but 
very  briefly  stated,  Ust  of  topics  or  subject  headings  concern- 
ing which  the  lecturer  has  spoken.  Then  copy  and  elaborate 
these  topics  before  the  next  lecture.  Use  your  topic  hst  as  a 
quiz  sheet,  asking  yourself  questions  about  each  one. 

(2)  Understand  the  topic  —  Do  not  try  to  remember  any- 
thing you  do  not  understand.  It  is  a  waste  of  energy  and 
results  are  of  no  value  to  you. 

(3)  Review  often  —  If  you  can,  study  your  lesson  at  two 
different  times,  that  is,  study  at  night  and  review  it  in  the 
morning  before  going  to  class.  Men  who  have  studied  the 
way  in  which  the  mind  works,  tell  us  this  review  helps  one  to 
remember. 

(4)  Concentrate  your  attention,  that  is,  keep  your  mind  on 
your  work,  instead  of  allowing  it  to  wander  to  the  conversa- 
tion of  others  or  to  things  happening  within  sight. 

*  Taken  in  part  from  a  sheet  of  directions  by  W.  C  Crouch. 


TO  THE  STUDENT  \li 

(5)  Study  away  from  interruption.  Have  a  definite  place 
for  study  where  you  will  not  be  interrupted. 

Regularity  of  time  for  study  also  helps. 

(6)  Recite  and  review  again.  Repeating  what  you  know  and 
reviewing,  are  the  most  important  factors  in  mastering  any 
subjects  whether  a  rule  in  mathematics,  a  topic  in  history,  or  a 
principle  in  science.  It  is  a  good  plan  to  review  hard  topics 
from  week  to  week. 


TABLE    OF    CONTENTS 

Page 

Title  Page i 

Preface  to  Third  Edition iii 

To  THE  Student v 


PART   I. 

SALTS    OF  THE   METALS   AND    QUALITATIVE  ANALYSIS. 

Chapter 

I.  Introduction i 

II.  Metals  and  Their  Salts 15 

III.   Salts  of  Grolt>  Ont  Metals 18 

Analysis  of  Group  One 24 

rv.  Salts  of  Grout  Two  ^Iet.als 26 

Special  Tests  for  Arsenic 34 

Analysis  of  Group  Two ; 47 

V.   Salts  of  Group  Three  ]\Ietals 53 

Analysis  of  Group  Three 58 

VI.   S.ALTS  of  Group  Four  Metals 61 

Analj'sis  of  Group  Four 66 

\TI.   S.ALTS  OF  Group  Fr-e  Metals .-.  69 

Analysis  of  Group  Five 75 

VIII.   Salts  of  Grout  Six  Met.als 7S 

Outline  Scheme  for  Analysis 90 

IX.  Analytical  Reactions  of  the  Acids 91 

X.  Analysis  in  the  Dry  \^'ay , 102 

PART  II. 

-      DENTAL   METALLURGY. 

XI.  Properties  of  the  Met.als iii 

XII.  Alloys 114 

XIII.  AiLALGAMS 119 

XIV.  Fusible  Metals  ant)  Solders 128 

XV.    DeNT.AL  CEilENTS 135 

X\T.   Reco\-ery  of  Residu-e 141 


E  TABLE  OF   CONTENTS 

PART  III. 

VOLUMETRIC   ANALYSIS. 

Chapter  Page 

XMI.   Standard  Solutions 143 

Quantitative  Analysis  of  Dental  Alloys 166 

PART  IV. 
MICROCHEMICAL   ANALYSIS. 

XVIII.  Methods 168 

XIX.  Local  Anesthetics  and  Antiseptics 173 

XX.  Teeth  and  Tart.\r 189 

PART  V. 

ORGANIC   CHEMISTRY. 

XXI.  The  Hydrocarbons  and  Substitution  Products 193 

XXII.  Alcohols 205 

XXIII.  Ethers 211 

XXIV.  Organic  Acids 216 

XXV.   Cyanogen  Compounds.    Sulphur  CoiLPouNDS 228 

XX\T.  Amines  or  Substituted  Ammonias 233 

XXVII.   Urea  and  Uric  Acid 237 

XXVTII.   Closed  Chain  Hydrocarbons 244 

PART  VI. 

PHYSIOLOGICAL   CHEMISTRY. 

XXIX.   Ferments  or  Enzymes 256 

XXX.   Carbohydrates 259 

XXXI.   Fats  and  Oils 265 

XXXII.   Proteins 269 

Simple  Proteins 275 

Conjugated  Proteins 280 

Derived  Proteins 284 

Blood  and  Muscle 286 

PART   VII. 
DIGESTION. 

XXXIII.  Properties  and  Constituents  of  Salfva 291 

XXXIV.  .Analysis  of  Saliva 3°4 

Crystals  from  Dialyzed  Saliva 316 

Tests  for  .\bnormal  Constituents 317 


TABLE  OF  CONTENTS  XI 

Chapter  Page 

XXXV.   Gastric  Digestion 319 

XXXVI.   P.\NCREATic  Digestion  and  Bile 321 

PART    VIII. 

URINE. 

XXXVII.   Physical  Properties  of  Urine 326 

XXX\'III.    XoR\I.VL   COXSTITXJENTS 33I 

XXXIX.   Abnormal  Constitlt:nts 343 

Urinar\-  Sediments 353 

Recording  Results 358 

PART   IX. 

METABOLISM. 

XL.  Metabolism 361 

Experiments 367 

Appendix  —  Reagents 424 

Appendix  —  Organic  Preparations 430 


DENTAL  CHEMISTRY. 


PART    I. 

SALTS  OF  THE  METALS   AND  QUALITATIVE  ANALYSIS. 


CHAPTER   I. 

INTRODUCTION. 

Every  science  has  a  language  peculiar  to  itself,  a  thorough 
understanding  of  which  is  an  essential  preUminary  to  the  study  of 
that  science.  Hence,  before  we  take  up  the  study  of  Dental 
Chemistry,  it  will  be  well  to  review  a  few  definitions  and  perhaps 
a  few  of  the  facts  of  Physics  which  are  closely  related  to  our 
subject. 

Definitions. 

Matter  has  been  divided  into  masses,  molecules,  atoms  and 
electrons,  and  we  are  to  study  first  the  properties  of  these  di- 
visions. For  purposes  of  present  definitions  it  may  be  necessary 
only  to  consider  that  aggregations  of  electrons  constitute  atoms; 
groups  of  atoms  make  up  the  molecules;  and  numbers  of  mole- 
cules held  together  by  the  physical  force  of  cohesion  form  masses. 
The  properties  of  these  divisions  of  matter  will  constitute  our 
further  definition. 

The  mass  is  any  quantity  of  matter  which  has  appreciable 
weight.  It  is  influenced  by  such  general  physical  laws  as  gravi- 
tation and  adhesion. 


2       SALTS  OF   THE  METALS  AND  QUALITATIVE  ANALYSIS 

The  molecule  has  been  defined  as  the  smallest  particle  of 
matter  that  can  exist  and  retain  the  properties  of  the  original 
substance,  or  the  smallest  particle  of  matter  into  which  a  sub- 
stance can  be  divided  by  physical  means.  This  however  gives 
us  no  picture  of  the  molecule.  To  obtain  this  we  must  consider 
the  facts  of  molecular  weight,  of  molecular  motion,  of  intermolec- 
ular  space  and  of  the  eft'ects  of  heat  and  cold ;  then  we  may  be 
able  to  see  the  reasons  for  some  of  the  things  we  have  already 
learned  about  the  behavior  of  chemical  substances. 

The  atoms  we  will  consider  as  the  smallest  particles  of  which 
the  molecule  is  composed.  Our  imagination  should  invest  the 
atoms  with  all  the  properties  of  the  molecule,  but  should  in- 
clude some  important  differences.  First:  the  molecules  of  a 
mass  are  supposed  to  be  all  exactly  alike  in  composition.  Second : 
they  are  attracted  to  one  another  in  the  same  way  and  to  the 
same  degree.  Third:  their  separation  from  one  another  does 
not  of  necessity  involve  disturbance  of  the  electrical  equiUbrium 
of  the  mass.  The  atoms  in  the  molecule  are  usually  (not  al- 
ways) of  different  kinds.  They  are  held  together  by  a  peculiar 
force  of  selective  attraction  formerly  called  chemism  or  chemical 
affinity;  and  electrically  considered  the  uncombined  atom  is 
supposed  to  be  either  positive  or  negative. 

The  electrons  are  the  infinitesimal  particles  of  which  the 
atoms  are  composed  and  have  been  regarded  as  constituting 
the  force  which  determines  their  character.  Professor  Harry 
C.  Jones  says  the  electrons  are  negative  charges  of  electricity, 
and  explains  their  role  in  the  theory  of  dissociation  as  follows: 
"  Take  a  salt  like  potassium  chloride.  When  it  is  thrown 
into  water  an  electron  passes  from  the  potassium  over  to  the 
chlorine.  The  chlorine  having  received  an  additional  electron 
thus  becomes  charged  negatively,  while  the  potassium  having 
lost  an  electron  becomes  charged  positively.  If  we  are  dealing 
with  bivalent  ions  we  have  simply  a  transfer  of  two  electrons. 
Take  barium  chloride.    The  barium  loses  two  electrons,  one  to 


INTRODUCTION  3 

each  of  the  chlorines;  the  latter  becoming  charged  negatively, 
while  the  barium  has,  consequently,  two  positive  charges  upon 
it."     The  mental  picture  may  be  difficult  but  it  is  very  necessary. 

Ions.  —  The  electrically  charged  particles  or  parts  of  mole- 
cules capable  of  attraction  to  either  cathode  or  anode  in  the 
process  of  electrolysis  have  been  called  ''  ions "  (Faraday's 
definition) .  Ions  may  consist  of  single  atoms  as  in  H"^C1~  or  of 
groups  of  atoms  (radicals)  as  in  water  H+(OH)~  or  ammonium 
hydrate  (XIl4)+(0H)~. 

The  molecule  of  an  element  consists  of  but  one  kind  of  atoms. 

The  molecule  of  a  compound  consists  of  two  or  more  elements 
chemically  combined. 

Symbols.  —  Sjonbols  are  used  to  designate  the  various  ele- 
ments. In  some  cases  the  initial  letter  of  the  element  alone  is 
used,  as  C  for  carbon.  In  other  cases  there  is  added  a  distinc- 
tive small  letter  of  the  name  when  there  happen  to  be  a  number 
of  elements  \nth  names  beginning  with  the  same  letter  such  as 
Calcium,  Ca;  Cobalt,  Co;  Copper,  Cu;  etc. 

Chemical  Formula.  —  A  chemical  formula  represents  the 
molecule  and  is  made  up  of  the  symbols  of  the  several  con- 
stituent elements.  Chemical  formulae  may  be  empirical,  dua- 
listic  or  graphic.  The  empirical  formula  represents  the  molecule 
without  reference  in  any  way  to  its  structure,  i.e.,  H2SO4. 

The  duaHstic  formula  indicates  compounds  which  may  enter 
into  the  composition  of  a  molecule.  By  this  sort  of  formula 
sulphuric  acid  would  be  represented  by  H0O.SO3. 

The  graphic  formula  attempts  to  show  the  probable  relation 
of  the  atoms  in  the  molecule  by  means  of  bonds,  e.g.. 

Valence.  ---  Valence  is  a  property  of  atoms  and  represents 
their  combining  power  relative  to  hydrogen  measured,  perhaps, 
by  loss  or  gain  of  electrons.     Valence  is  not  always  constant  for 


4       SALTS  OF  THE  METALS  AND  QUALITATIVE  ANALYSIS 

the  same  elements;  for  example,  sulphur  has  a  combining  power 
of  six  in  sulphuric  acid,  of  four  in  sulphur  dioxide  and  of  two 
in  hydrogen  sulphide.  Nitrogen  has  a  combining  power  of 
three  in  ammonia  gas  and  five  in  ammonium  chloride.  Valence 
has  also  been  indicated  by  the  terms  quantivalence  and  atomicity. 

Acid.  —  An  acid  is  a  compound  capable  of  producing  upon 
ionization  positive  hydrogen  ions  which  may  be  replaced  by  a 
metallic  element  or  radical.  The  more  common  acids  are  sour 
to  the  taste  and  act  in  characteristic  manner  upon  a  number  of 
color  compounds  known  as  indicators. 

Base.  —  A  base  is  a  substance  capable  of  producing,  upon 
ionization,  negative  hydroxyl  ions  which  may  be  replaced  by 
acid  radicals.  Bases  in  general  characteristics  oppose  acids. 
The  strongest  bases  are  known  as  alkalies,  e.g.,  KOH,  NaOH. 

A  Salt.  —  A  salt  is  a  substance  produced  by  the  chemical 
union  of  an  acid  and  a  base. 

In  the  formation  of  the  salt  the  acid  may  not  have  been 
completely  neutralized  by  the  base  and  an  acid  salt  results.  In 
such  a  case  the  salt  contains  a  part  of  the  hydrogen  ions  of  the 
acid,  e.g.,  potassium  acid  sulphate,  KHSO4,  the  production  of 
which  may  be  represented  by  the  equation 

KOH  +  H2SO4  =  KHSO4  +  H2O. 

Acid  salts  may  or  may  not  have  acid  properties  such  as  sour 
taste  and  power  to  give  acid  reactions  with  indicators,  for  ex- 
ample NaHCOs,  chemically  an  acid  salt,  is  alkaline  to  litmus  and 
has  other  physical  properties  of  the  bases.  This  fact  is  explained 
by  the  hydrolysis  of  the  salt,  hydrolysis  being  the  utiHzation  of 
the  ionized  water  molecule.  The  condition  may  be  represented 
as  follows: 

NaHCOa^  Na+  +  HCO~ 

H2O  ^  OH"  +  H+ 

it  it 

NaOH     H2CO3. 


INTRODUCTION  5 

If  the  add  is  exactly  neutralized  by  the  base,  neutral  sails 

result. 

2  NaOH  +  H2SO4  =  Na2S04  +  2  H2O. 

A  salt  may  on  the  other  hand  be  basic  and  contain  a  portion  of 
the  hydroxyl  ions  (or  sometimes  oxygen  atoms)  of  the  base. 

Example:  Bi(0H)3  +  2  HNO3  =  BiOH(N03)2  +  2  H2O  or 
BiCls  +  H2O  =  BiOCl  +  2  HCl. 

Reactions  between  cheinical  substances  may  be  "  completed  " 
or"  reversible." 

A  completed  reaction  is  one  which  progresses  in  a  definite 
way  irrespective  of  changes  in  temperature  of  the  quantities 
of  the  reacting  substances;  or,  a  completed  reaction  is  one  in 
which  one  of  the  products  is  chemically  inactive.  This  inac- 
tivity may  be  due  to  one  of  several  causes,  such  as  the  production 
of  an  insoluble  precipitate;  e.g.,  AgCl  in  the  reaction, 

AgNOs  +  NaCl  =  AgCl  -f-  NaNOs, 

or  the  escape  of  the  product  as  a  gas  and  its  consequent  removal 
from  solution  —  as  when  carbonates  are  dissolved  by  acid. 

The  reversible  reaction  is  one  in  which  the  products  remain 
to  a  greater  or  less  degree  in  solution  and  a  change  of  temperature 
or  increase  in  quantity  of  one  of  the  products  may  start  a  reverse 
reaction;  for  example,  at  the  body  temperature,  dibasic  sodium 
phosphate  and  uric  acid  may  become  monobasic  sodium  phos- 
phate and  acid  sodium  urate, 

Na2HP04  +  H2U  =  NaH2P04  +  NaHU, 

while  at  reduced  temperature, 

NaH2P04  +  NaHU  =  Na2HP04  +  H2U.     (See  page  242.) 

Reversible  reactions  are  expressed  by  use  of  the  sign  <=^; 
thus,  MgCl2  +  2  NH4OH  T±  Mg(0H)2  +  2  NH4CI.  The  reac- 
tion may  be  expressed  as  an  equation  if  we  know  what  substances 
take  part  in  the  reaction  and  what  products  are  formed.     The 


6       SALTS  OF   THE  METALS  AND  QUALITATIVE  ANALYSIS 

above  reaction  can  be  balanced  at  a  glance  and  is  therefore  not 
well  suited  for  illustration  but  the  use  of  a  little  more  complex 
equation  will  show  how  easily  it  can  be  balanced  by  a  few  al- 
gebraic combinations. 

Cu  +  HNO3  =  Cu(N03)2  +  NO  +  H2O. 
Represent  all  these  as  unknown  quantities. 

xCn-{-y  HNO3  =  z  Cu(N03)2  +  m  NO  +  p  H2O, 
then 


X  Cu  =  z  Cu 
yU    ^pU2 

yN    =z  (N)2  +  w  N 

yOs  =z  (03)2  +  w  O  +  ^  O 


X  =  Z  (l) 

Q^    y  =  2p  (2) 

y  =  2  z  -{-  m  (3) 

T,y  =  6z  +  in-\-p  (4) 


multiplying  equation  3  by  3,  3  }>  =  6  z  +  3  ??^  (5) 

and  by  elimination  (4  and  $),  2  m  =  p  (6) 

and  4  m  =  2  p,  then  by  eq.  2,  y  =  4.m  (7) 

assuming  that  w  =  i,  then,  in7,y  =  4;  'm6,p  =  2;  in  3,  2  z  =3, 


or  z  =  I 


in  1,  X  =  i^.  Knowing  that  all  equations  must  be 
expressed  by  whole  numbers  we  double  these  values  and  have 
X  =  T,,  y  =  S,  z  =  2,,  m  =  2,  p  =  4. 

Upon  substituting  these  values  we  shall  find  that  the  equation 
"  balances." 

Theoretical  Considerations.* 

In  order  to  understand  the  phenomena  of  solution  and  precip- 
itation it  will  be  necessary  to  include  in  our  review  a  few  of  the 
terms  of  theoretical  chemistry  such  as  Phase  —  Physical  Equi- 
librium —  Mass   Action  —  Chemical   Equihbrium  —  Ionization. 

The  term  Phase  refers  to  the  condition  in  which  a  substance 
exists:  soHd,  gaseous,  hquid,  crystalline.  So  sulphur  is  said  to 
exist  in  four  phases,  water  in  three.    ■ 

The  term  Equilibrium  conveys  the  idea  of  equaUty  between 

*  It  is  usually  desirable  that  the  study  of  this  chapter  be  accompanied  by 
very  thorough  lecture  room  explanations  and  laboratory  demonstration.  See 
page  367. 


INTRODUCTION  7 

opposing  forces  resulting  in  stability,  e.g.,  the  water  in  a  closed 
bottle  tends  to  evaporate;  the  tension  or  pressure  of  the  vapor 
tends  to  prevent  evaporation.  When  the  one  force  equals 
the  other  equiUbrium  results.  Another  example,  illustrating 
the  meaning  of  physical  equilibrium  and  at  the  same  time 
showing  why  concentration  is  so  often  useful  in  producing  pre- 
cipitates which  may  be  easily  filtered,  is  given  by  StiegUtz  *  as 
follows:  "  If  a  crystalline  precipitate  is  in  contact  with  a  solvent, 
e.g.,  if  barium  sulphate  is  in  contact  with  the  Hquid  from  which 
it  has  been  precipitated,  then  this  liquid  must  be  continually 
in  a  state  of  change,  not  of  equiHbrium,  with  respect  to  the 
solution  and  the  deposited  barium  sulphate.  The  more  minute 
crystals,  being  a  Httle  more  soluble  than  the  larger  ones,  will 
supersaturate  the  solution  in  respect  to  the  larger  crystals  and 
the  excess  will  be  deposited  on  these  larger  crystals  and  make 
them  grow  still  larger.  This  deposition  will  make  the  solution 
unsaturated  with  respect  to  the  smaller  crystals  and  more  of 
these  will  dissolve.  The  process  is  obviously  a  continuous  one, 
and  must  lead  in  time  to  the  disappearance  of  the  minute  crystals 
and  the  growth  of  the  larger  ones." 

Ionization  has  been  defined  on  page  3,  but  a  further  con- 
sideration of  the  subject  is  necessary  if  we  would  imderstand  its 
effect  on  chemical  reaction.  The  following  important  facts  have 
been  demonstrated  regarding  the  theory. 

The  dissociated  ions  of  the  molecule  are  capable  of  migration 
and  wiU  collect  at  the  poles  of  a  battery  according  to  the  well- 
known  laws  of  magnetic  attraction:  the  positive  ion  (cation, 
or  metal  ion)  going  to  the  negative  pole,  while  the  negative  ion 
(anion,  or  acid  ion)  goes  to  the  positive  pole. 

Dilution  of  the  solution  increases  the  degree  of  ionization. 

Substances  which  ionize  increase  the  electrical  conducti\aty 
of  the  solution,  and  the  measure  of  the  conductivity  is  a  measure 
of  the  degree  of  ionization. 

*  Qualitative  Chemical  Analysis. 


8       SALTS  OF  THE  METALS  AND  QUALITATIVE  ANALYSIS 

A  given  substance  may  ionize  differently  under  different 
conditions,  e.g.,  phosphoric  acid  may  ionize  as  H+  and  (H2P04)~ 
or  as  H+.H+  and  (H.P04)~,  or  as  H+H+H+  and  (PO4)".  The 
negative  ion  of  sulphuric  acid  may  be.(HS04)~  or  (S04)~.  The 
various  atoms  of  hydrogen  of  an  acid  do  not  ionize  with  equal 
facihty  and  the  terms  primary,  secondary,  and  tertiary  ioni- 
zation may  be  appHed  to  such  cases  as  the  above  example  of  the 
ionization  of  phosphoric  acid. 

The  actixity  of  a  reagent  depends  upon  the  number  of  free 
ions  in  solution. 

Reaction  between  non-ionized  molecules  takes  place  very 
slowly. 

Water  is  the  most  important  ionizing  solvent.  The  alcohols 
cause  less  ionization,  and  the  saturated  hydrocarbon  compounds 
as  Benzene,  Chloroform,  or  Gasolene,  very  little  indeed. 

Water  itself  hydrolyzes  to  a  sHght  extent  and  the  utilization 
of  the  water  ions  in  forming  new  molecules  constitutes  "Hy- 
drolysis." 

Complex  ions  may  themselves  be  ionized  in  the  presence  of 
other  ionizable  compounds. 

Mass  Action.  —  The  quantity  of  the  reagent  has  long  been 
recognized  as  a  factor  in  chemical  reaction,  e.g.,  nitric  acid 
will  replace  hydrochloric  acid  in  combination  if  the  nitric  acid 
is  in  sufficient  excess,  or  if  the  hydrochloric  acid  is  in  excess 
the  reverse  reaction  may  take  place.  The  completion  of  a 
reaction  is  often  impossible  wdthout  excess  of  one  or  the  other  of 
the  substances  involved.  The  precipitation  of  insoluble  salts 
depends  in  many  cases  upon  the  quantity  of  reagent  available 
which  in  turn  may  depend  upon  the  degree  of  ionization. 

The  application  of  these  facts  to  the  study  of  the  deposition 
of  tartar  is  one  of  our  present  problems. 

Chemical  Equilibrium.  —  On  page  5  we  saw  how  a  certain 
reagent  might  act  in  a  given  way  or  the  reverse  according  to  the 
temperature  employed.     If   we    couple    this  idea  of   chemical 


INTRODUCTION  9 

activity  with  the  one  given  in  the  preceding  paragraph  we  can 
easily  picture  conditions  which  will  result  in  chemical  equilib- 
rium (not  inactivity).  This  has  been  defined  as  the  point  at 
which  two  opposite  reactions  acquire  the  same  velocity.* 

Solution  and  Precipitation. 

"Solution  is  the  equal  distribution  of  a  body  in  a  liquid, 
the  resulting  mass  being  in  all  parts  homogeneous  and  fluid 
enough  to  form  drops,"  according  to  an  old  definition  quoted 
in  *'  Colloids  and  the  Ultramicroscope  "  by  Dr.  Richard  Zsig- 
mondy. 

We  can  readily  adopt  this  definition  for  present  use  provided 
our  conception  of  homogeneity  is  sufficiently  elastic  to  include 
"  Colloidal  "  solutions,  and  if  we  remember  that  the  fluidity  is 
not  necessarily  permanent  as  we  have  a  number  of  recognized 
sohd  solutions  among  the  alloys.     See  Chapter  XII. 

The  Law  of  Partition.  —  If  two  immiscible  solvents  of  a 
given  substance  are  brought  together  the  amount  of  the  sub- 
stance held  in  solution  by  each  solvent  will  be  in  proportion  to 
the  solubiHty  of  the  substance  in  each  solvent  respectively,  e.g., 
Fe(CyS)3  is  more  soluble  in  ether  than  in  water,  hence  in  a  mix- 
ture of  water  and  ether  a  proportionately  larger  amount  of  the 
salt  would  be  dissolved  by  the  ether. 

The  solvate  theory  of  solution  of  Professor  H.  C.  Jones  f 
is  briefly,  that  soluble  substances  form  a  large  number  of  defi- 
nite compounds  with  the  solvent;  that  the  number  and  com- 
plexity of  these  hydrates  diminish  as  the  concentration  of  the 
solution  increases  or  as  the  temperature  rises;  and  that,  for  the 
most  part  the  union  is  betweeii  the  solvent  and  the  ions,  rather 
than  the  molecules,  of  the  dissolved  substance. 

*  Jones,  "  New  Era  in  Chemistry,"  p.  28. 

t  This  theory  is  explained  in  detail  in  Professor  Jones'  book  "  A  New  Era 
in  Chemistry,"  Chapter  IX. 


lO      SALTS  OF   THE  METALS  AND  QUALITATIVE  ANALYSIS 

The  colloids  are  distinguished  from  crystalloids  by  their 
inability  to  pass  through  parchment  membrane.  In  coUoidal 
solutions  the  substance  (colloid)  may  be  considered  as  in  sus- 
pension or  a  state  of  subdivision  so  nearly  complete  as  to  ap- 
proach closely  to  the  homogeneity  of  crystalloidal  solution. 

In  many  colloidal  solutions  the  particles  are  large  enough  to 
interfere  with  the  passage  of  light  and  the  preparation  is  more  or 
less  opaque.  In  some,  however,  this  is  not  noticeable  except 
by  use  of  polarized  hght  and  special  apparatus. 

There  is  no  sharply  defined  Hne  between  the  suspensions  and 
the  colloidal  solutions,  and  it  is  often  true  that  the  homogeneity 
of  a  solution  is  dependent  upon  the  "  grossness  of  our  means  of 
observ^ation."     (Zsigmondy.) 

CoUoidal  substances  as  a  class  may  be  separated  from  the 
crystalloids  by  Dialysis,  animal  membrane  suspended  in  dis- 
tilled water  being  used  as  a  separating  medium.  The  crystal- 
loids will  pass  through  the  membrane  into  the  pure  water, 
while  the  colloids  remain  behind.  The  use  of  the  dialyzer  as 
applied  to  saliva  analysis  is  shown  on  page  316. 

Osmosis  signifies  the  passage  of  water  only  through  a  mem- 
brane, tending  to  correct  inequalities  of  pressure  produced  by 
diflferences  in  molecular  concentrations  of  two  solutions. 

This  is  usually  illustrated  by  dropping  potassium  f errocyanide 
solution  into  copper  sulphate.  The  drop  of  potassium  ferro- 
cyanide  becomes  surrounded  by  a  film  of  copper  f errocyanide, 
through  which  water  alone  will  pass.  Membrane  of  this  charac- 
ter is  known  as  semipermeable. 

Porous  cups  are  prepared  for  demonstrations  of  osmosis  by 
precipitating  within  the  pores  of  the  cup  or  cell  the  ferrocyanide 
of  copper. 

Osmotic  pressure  is  the  pressure  produced  within  a  semi- 
permeable cell  by  passage  of  water  from  the  outside;  or,  as 
stated  by  Holland,  it  is  "  That  push  of  the  molecules  of  a  solute 
upon  its  solvent  which  causes  a  flow  through  a  membrane  into 
the  solution." 


INTRODUCTION  II 

Precipitation  signifies  throwing  out  of  a  substance  in  solid 
form  from  solutions.  The  precipitation  may  be  brought  about 
in  three  ways: 

First,  by  change  of  temperature,  when  the  substance  pre- 
cipitated is  the  same  as  that  previously  held  in  solution; 

Second,  by  change  in  the  character  of  the  solvent,  which 
likewise  involves  no  chemical  change  and  hence,  like  the  first, 
may  be  regarded  as  a  physical  method. 

The  third  method  depends  upon  the  formation  of  a  new  sub- 
stance and  is,  of  course,  a  chemical  method. 

Illustrations,  —  First  method:  The  separation  of  crystals  of 
lead  chloride  by  cooling  a  hot  solution  of  the  salt. 

Second  method:  Precipitation  of  barium  chloride  from  saturated 
solution  by  strong  hydrochloric  acid. 

Third  method:    Any  double  decomposition  resulting  in  the 
formation  of  an  insoluble  compound. 

'  Weights  and  Measures 

Measures.  —  The  metric  system  of  weights  and  measures 
and  the  Centigrade  thermometer  are  largely  used  in  all  scientific 
work.  The  dentist,  however,  has  also  considerable  use  for 
troy  weights  and  apothecaries'  measures  if  he  considers  at  all 
the  composition  of  his  gold  solders,  dental  alloys,  mouth  washes, 
local  anesthetics,  etc.  Hence,  a  few  equivalents  are  here 
given. 

The  meter  is  the  primary  unit  of  the  metric  system  and  was 
originally  calculated  as  one  ten-millionth  part  of  the  quadrant 
from  the  equator  to  the  pole. 

I    meter  =  loo    centimeters,  =  looo    millimeters    or    39.37 

inches. 
I  centimeter  =  10/25  or  0.3937  ^^  2,n  inch. 
I  cubic  centimeter  =  16.23  minims  or  0.0338  of  a  fluid  ounce. 
1000  cubic  centimeters  (c.c.)  =  i  liter  or  2.1 13  pts. 


12      SALTS  OF   THE  METALS   AND  QUALITATIVE  ANALYSIS 

The  weight  of  i  c.c.  of  pure  water  at  the  temperature  of  its 
greatest  density  (4°  C.)  is  taken  as  a  unit  of  weight  and  called 
a  gram  (gramme). 

I  gram  =    15.43  grains. 

1000  grams  =  i  kilogram  (kilo)  =  35  oz.  120  grains  or  2.2 

lbs.  avoir. 
I  inch  =  2.54  centimeters  or  25.4  millimeters. 
I  oz.  av.  =  28.3495  grams  or  437.5  grains. 
I  fluid  oz.  =  8  fluid  drams,  29.57  c-c,  or  456  grains  of  water. 
I  fluid  dram  =  3.7  c.c. 
I  troy  oz.  =  8  drams  (5)  or  480  grains. 
I  troy  oz.  =  24  scruples   (3)   or  20  pennyweight   (pwt.   or 

dwt.). 
I  scruple  =  20  grains,  i  pennyweight  =  24  grains. 
I  grain  =  64  milligrams. 
I  pint  =  473.11  c.c. 

I  gallon  =  8  pints,  or  3785  c.c,  or  231  cubic  inches. 
I  lb.  avoir.  =  7000  grains  or  453.59  grams. 

Measure  of  Temperature.  —  We  shall  constantly  meet  ref- 
erence to  both  the  Centigrade  and  Fahrenheit  scales  and  an 
understanding  of  the  relationship  of  the  two  methods  is  essential. 

The  thermometer  is  graduated  by  marking  the  point  at  which 
the  mercury  stands  when  the  instrument  is  placed  on  melting 
ice;  and  again  the  point  reached  by  the  mercury  when  the 
thermometer  is  surrounded  by  dry  steam  under  ordinary  at- 
mospheric conditions. 

On  the  Centigrade  thermometer,  the  lower  or  freezing  point 
is  marked  zero,  the  upper  or  boiling  point  is  marked  one  hundred, 
and  the  intervening  space  divided  into  one  hundred  equal  de- 
grees. On  the  Fahrenheit  scale,  these  points  are  marked  respec- 
tively 32  and  212  and  the  scale  is  divided  into  180°;  hence, 
1°  C.  equals  1.8°  or  9/5°  Fahrenheit,  and  1°  F.  equals  5/9  of 
a  Centigrade  degree.     Providing  for  the  different  freezing  points 


INTRODUCTION  1 3 

(0°  and  32°),  we  can  formulate  a  rule  for  converting  tempera- 
ture records  from  one  scale  to  the  other,  as  follows: 

To  convert  Centigrade  to  Fahrenheit,  take  9/5  of  the  given 
number  of  degrees  and  add  32. 

To  convert  Fahrenheit  to  Centigrade,  subtract  32  from  the 
given  number  and  take  59  of  the  remainder;  e.g., 

20°  C.  =  68°F. 
-5°C.  =  +23^  F. 
77°F.  =  25°  C. 
14°  F.  =  -io°C. 

Absolute  Temperature. 

According  to  the  Law  of  Charles  or  of  Gay-Lussac,  gases 
(free  molecules)  contract  1/273  of  their  volume,  measured  at 
0°  C,  for  every  Centigrade  degree  that  the  temperature  falls; 
so  it  is  assumed  that,  at  a  point  273°  below  the  Centigrade  zero, 
no  further  contraction  would  be  possible,  molecular  motion 
would  cease  and  all  things  become  soHd.  This  temperature  has 
been  called  the  absolute  zero  and  temperature  recorded  from 
this  point  absolute  temperature;  thus,  water  freezes  at  273°  C. 
absolute  temperature. 

Gea\t:ty. 

Specific  gra\ity  is  the  relative  weight  of  equal  bulks  of 
different  substances,  one  of  which  is  taken  as  a  standard. 

The  standard  is  usually  water  for  hquids  and  sohds. 

The  standard  for  gases  may  be  air  or  hydrogen. 

WTien  gases  are  referred  ta  hydrogen  as  a  standard,  the  term 
density  is  often  used  instead  of  specific  gra\-ity,  and,  to  avoid  con- 
fusion, this  usage  is  recommended;  i.e.,  the  density  of  carbon 
dioxide  is  22,  while  its  specific  gravity  compared  with  air  is 
about  1.53. 


14      SALTS  OF   THE  METALS  AND  QUALITATIVE  ANALYSIS 

The  density  of  a  gas  will,  according  to  the  Law  of  Avogadro, 
be  one-half  its  molecular  weight. 

The  specific  gravity  of  a  Uquid  may  be  diminished  by  the 
solution  of  a  gas,  as  in  case  of  solution  of  ammonia;  or  it  may 
be  increased,  as  in  case  of  solution  of  hydrochloric  acid. 

The  boiling  point  of  a  Hquid  is  raised  by  the  solution  of  solids, 
and  often  by  the  solution  of  gases. 

Cryoscopy. 

The  freezing  point  of  liquids  is  lowered  by  the  solution  of 
other  substances.  As  the  amount  of  reduction  of  temperature 
necessary  to  change  the  liquid  to  the  solid  has  been  found  to  be 
in  direct  proportion  to  the  amount  of  dissolved  substance,  it 
becomes  possible  to  make  many  valuable  determinations  by 
this  method.  For  accurate  work,  it  is  necessary  to  use  a  special 
thermometer  graduated  into  hundredths  of  a  degree.  The  use 
of  the  freezing  point  of  a  solution  in  determining  the  amount  of 
the  dissolved  substance  is  known  as  cryoscopy,  and  is  of  great 
importance  in  both  physical  and  physiological  chemistry. 


CHAPTER  II. 
THE  METALS   AND   THEIR   SALTS. 

Qualitative  Analysis. 

The  metals  occur  free  in  nature  to  quite  an  extent,  but  more 
often  combined  ^^'ith  other  elements.  These  combinations  are 
chiefly  as  oxides,  sulphides,  carbonates  and  silicates,  and  in  one 
or  more  of  these  four  forms  the  great  mass  of  metals  contained 
in  the  earth's  crust  may  be  found. 

]\Ietallic  sulphates  are  found  to  a  considerable  extent. 

Other  natural  sources  of  the  metals  are  phosphates  and  chlo- 
rides, also  smaller  amounts  of  nitrates  and  comparatively  sHght 
amounts  of  bromides,  iodides  and  fluorides.  Metals  are  ex- 
tracted from  their  ores  chiefly  by  reduction  with  some  form  of 
carbon.  In  case  of  the  oxides  this  reduction  takes  place  directly, 
according  to  this  reaction:   2  CuO  +  C  =  2  Cu  -f  CO2. 

In  case  the  metallic  combination  is  a  sulphide,  the  ore  is  first 
"  roasted  "  in  the  air,  whereby  the  sulphur  is  burned  off  and  an 
oxide,  which  may  then  be  reduced  as  above,  is  formed: 
2  CuS  +  3  O2  =  2  CuO  -j-  2  SO2. 

The  native  carbonates  are  reduced  to  oxides  by  calcination,  as 
CaCOs  +  heat  =  CaO  +  CO2. 

The  silicates  must  first  be  changed  to  carbonates  by  fusion 
with  alkali  carbonates ;  then  the  reduction  may  be  carried  on  as 
before: 

MgSiOs  +  NazCOs  =  MgCOs  +  Na^SiOs; 
MgCOg  +  heat  =  MgO  -|-  CO2. 

The  metals,  from  certain  physical  properties,  have  been  vari- 
ously classified.     Thus,  in  the  older  books  we  read  of  the  Noble 

IS 


l6      SALTS  OF   THE  METALS  AND  QUALITATIVE  ANALYSIS 

metals,  those  unaffected  by  heat,  as  gold,  silver,  and  platinum; 
the  Base  metals,  such  as  iron;  the  Bastard  metals,  those  easily 
crystallizable,  as  antimony  and  zinc;  the  Metalloids,  sodium  and 
potassium. 

As  the  fact  that  the  properties  of  metals  were  to  a  con- 
siderable extent  dependent  upon  conditions  of  temperature  and 
pressure  became  better  understood,  other  classifications  came  to 
be  used,  and  we  may  group  them  according  to  the  chemical 
behavior  of  their  salts,  irrespective  of  their  properties  as  metals. 
Thus  Ag,  Pb,  and  Hg  (mercurous)  form  a  group  of  metals 
whose  chlorides  are  insoluble  in  water  or  dilute  acids.  These 
metals  may  consequently  be  thrown  out  of  solution  or  precipi- 
tated by  the  addition  of  HCl  to  any  solution  of  their  salts.  We 
therefore  let  Ag,  Hg',  and  Pb  constitute  the  First  Analytical 
Group,  and  HCl  is  the  First  Group  Reagent. 

In  like  manner  we  find  a  group  of  nine  metals  that  are 
precipitated  from  dilute  acid  solution  by  hydrosulphuric  acid 
(H2S).  These  metals  are  Cu,  Cd,  Bi,  Hg,  As,  Sb,  Sn,  Au,  and 
Pt,  and  constitute  the  Second  Analytical  Group,  and  H2S  is  the 
Second  Group  Reagent. 

The  fact  that  the  sulphides  formed  by  the  first  four  of  these 
metals  are  insoluble  in  ammonium  sulphide,  and  those  formed 
by  the  last  five  are  soluble,  furnishes  a  simple  method  of  separat- 
ing this  group  into  two  parts,  a  and  b: 

Pb,*  Cu,  Cd,  Bi,  and  Hg  constituting  Group  H   (a)  and 

As,  Sb,  Sn,  Au,  and  Pt,  Group  H  (b). 

Thus,  the  metals  are  di\ided  into  various  analytical  groups, 
each  with  its  own  peculiar  group  reagent.  Different  groupings 
are  possible,  and  hardly  any  two  analysts  will  employ  exactly 
the  same  scheme  for  identifying  all  the  metals,  although  the 
following  group  divisions  are  generally  used: 

*  Lead  is  included  in  this  group  because  it  is  not  entirely  separated  as^  a 
chloride  in  Group  I,  traces  of  it  remaining  in  solution  even  after  addition  of  HCl. 


THE  METALS  AND   THEIR  SALTS  17 

Analytical  Groups. 

Group  I.  —  Ag,  Pb,  and  Hg'.  Metals  that  form  insoluble 
chlorides  and  are  precipitated  from  aqueous  solution  by 
HCl  (the  group  reagent). 

Group  II  (a).  —  Cu,  Cd,  Bi,  Hg",  and  Pb.  Metals  that 
form  sulphides  insoluble  in  dilute  HCl  solution  and  also 
insoluble  in  ammonium  sulphide. 

Group  II  {h).  —  As,  Sb,  Sn,  Au,  and  Pt.  Metals  that  form 
sulphides  insoluble  in  dilute  HCl  but  soluble  in  yellow 
ammonium  sulphide,  or  alkaline  hydrates. 

Group  III.  —  Fe.  Al,  and  Cr.  In  solutions  free  from  H2S 
and  which  do  not  contain  phosphates,  oxalates,  tartrates, 
or  salts  of  certain  other  organic  acids  these  three  metals 
may  be  separated  by  ammonium  hydrate  (NH4OH). 

Group  IV.  —  Co,  Xi,  ^In,  and  Zn.  ^Metals  forming  sulphides 
soluble  in  acid  but  insoluble  in  alkaline  solution.  Ammo- 
nium sulphide,  (XH4)oS,  is  the  group  reagent. 

Group  V.  —  Ba,  Sr,  Ca,  and  Mg.*  Metals  forming  car- 
bonates, insoluble  in  alkaline  solutions.  The  group  re- 
agent is  ammonium  carbonate,  (NH4)2C03. 

Group  Yl.  —  K,  Na,  Li,  NH4.  Metals  which  cannot  be 
precipitated  by  any  single  reagent  and  for  which  it  is 
necessary  to  make  indi\idual  tests. 

It  is  our  purpose  to  take  up  the  study  of  the  metals  according 
to  their  analytical  grouping:  first,  the  deportment  of  their 
salts  in  solution;  later,  the  metals  themselves  and  their  specific 
application  to  dentistry. 

*  In  the  process  of  analysis,  magnesium  is  held  in  solution  by  the  presence  of 
NH4CI  and  is  not  thrown  out  as  a  carbonate  with  the  other  three  members  of  the 
group. 


CHAPTER  III. 
METALS   OF    GROUP  I. 

Silver,  Ag  (Argentum). 

The  Metal.  —  Atomic  weight  107.88.  Silver  occurs  free  in 
masses  usually  containing  gold  and  copper;  as  sulphides,  such 
as  silver  glance  (Ag2S)  and  in  combination  with  sulphides  of 
antimony,  lead,  and  copper.  It  also  occurs  as  silver  chloride, 
(AgCl)  known  as  "  Horn  Silver  "  or  Kerargyrite. 

Properties.  —  Silver  fuses  at  954°  C,  forming  a  revolving 
globule  on  charcoal  or  plaster  without  oxidation. 

At  high  temperatures,  however,  silver  occludes  or  absorbs 
oxygen  to  the  extent  of  twenty- two  times  its  volume ;  but  as  the 
mass  cools  the  absorbed  gas  is  entirely  given  off,  sometimes 
resulting  in  a  roughened  surface  of  the  metal. 

This  property  may  be  overcome  by  alloying  with  copper  or 
by  covering  with  a  considerable  layer  of  common  salt. 

Silver  blackens  in  the  presence  of  sulphur  or  hydrogen  sul- 
phide. The  so-called  oxidized  silver  is  a  result  of  heating  the 
metal  with  a  solution  of  potassium  sulphide. 

Silver  dissolves  in  hot  H2SO4  with  evolution  of  SO2.  It  is 
readily  soluble  in  nitric  acid  with  formation  of  AgNGs,  colorless 
crystals,  without  water  of  crystallization. 

Silver  amalgamates  readily,  and  the  "  amalgamation  process  " 
is  one  of  the  important  methods  for  its  reduction  from  the  ore. 

This  process,  briefly,  is  as  follows: '  The  ore  is  roasted  with 
salt,  producing  chloride  of  silver;  this,  in  suspension  in  water,  is 
reduced  by  metallic  iron, 

2  AgCl  -\-¥e  =  FeClo  -f  2  Ag. 


METALS  OF  GROUP  I  19 

The  mixture  treated  with  mercury  forms  an  amalgam  from 
which  the  mercury  can  be  driven  off  by  heat. 

Alloys.  —  Important  alloys  of  silver  are  United  States  coin 
silver,  consisting  of  silver  90  parts,  copper  10  parts;  and  Sterling 
silver  consisting  of  silver  92.5  parts,  copper  7.5  parts. 

Amalgam  alloys  contain  from  50  to  60%  of  silver,  alloyed 
with  tin  and  sUght  amounts  of  other  metals  such  as  copper,  zinc, 
and  gold.     (See  page  125.) 

A  silver  platinum  alloy  used  for  base  plates,  clasps,  etc.,  con- 
tains from  12  to  35%  platinum  and  is  much  harder  than  pure 
silver. 

Von  Eckart's  alloy,*  a  French  preparation,  used  for  a  similar 
purpose,  contains  3.53  parts  silver,  2.40  parts  platinum,  and 
1 1. 7 1  parts  copper.  Silver  solders  are  alloys  of  varying  propor- 
tions of  silver,  copper,  and  zinc,  the  silver  running  from  60  to 
80%. 

Compounds.  —  Salts  of  silver  are  liable  to  decomposition  by 
action  of  light  with  reduction  in  greater  or  less  degree  to  metallic 
silver.  The  salts  change  from  violet  to  black  according  to  the 
amount  of  silver  reduced.  Such  reduction  is  illustrated  in  the 
use  of  the  ordinary  photographic  plates  and  paper. 

Silver  oxide  (Ag20) ,  a  dark  brown  powder,  may  be  produced 
in  the  wet  way,  i.e.,  by  precipitation  of  soluble  silver  salts  with 
hydroxides  of  the  fixed  alkalis. 

2  AgNOs  +  2  NaOH  =  AgaO  +  H2O  +  2  NaNOs. 

Silver  hydroxide  (white)  may  be  formed  if  the  above  reaction 
is  brought  about  in  alcoholic  solution;  but  it  is  a  very  unstable 
compound,  quickly  changing  to  Ag20  -|-  H2O.  Silver  thiosul- 
phate,  Ag2S203,  may  be  precipitated  white  from  solution  of  silver 
nitrate  and  sodium  thiosulphate.  Excess  of  the  thiosulphate 
produces  a  soluble  double  salt  NaAgS203.  This  fact  may  be 
utilized  in  the  removal  of  silver  stains. 

*  Hepburn,  page  60. 


20      SALTS  OF   THE  METALS  AND  QUALITATIVE  ANALYSIS 

Fused  silver  nitrate  in  the  form  of  pencils  or  small  sticks  is 
used  as  an  escharotic,  and  is  known  as  "  Lunar  Caustic."  Dilute 
lunar  caustic  consists  of  equal  parts  of  AgNOa  and  KNO3  fused 
together  in  pencil  form. 

Analytical  Reactions.  —  Make  the  following  tests  with  a 
weak  solution  of  AgNOa  (about  2%).  Write  the  reactions  and 
enter  color  and  solubihty  of  each  precipitate  formed  in  labora- 
tory note-book.* 

AgNOa  with  HCl  gives  a  white  curdy  precipitate  of  AgCl 
which  darkens  by  action  of  sunlight.  If  Ag  solution  is  very 
dilute,  the  precipitate  will  assume  the  curdy  appearance  and  filter 
more  easily  if  it  is  heated  and  rotated  quite  rapidly  in  the  test- 
tube.  Allow  the  precipitate  to  settle.  Decant  the  liquid  care- 
fully, divide  precipitate  into  two  parts,  and  test  its  solubihty 
in  dilute  nitric  acid,  also  in  ammonia  water. 

AgNOs  with  KBr  gives  a  white  precipitate  of  AgBr,  less 
easily  soluble  in  ammonia  than  the  AgCl. 

AgNOa  with  KI  gives  a  pale  yellow  precipitate  of  Agl, 
insoluble  in  ammonia. 

AgNOa  with  H2S  gives  a  black  precipitate  of  AgoS.  AgNOs 
with  K2Cr04  gives  a  red  precipitate  of  Ag2Cr04  in  neutral  solu- 
tion. Test  the  solubihty  of  Ag2Cr04  in  NH4OH,  HCl,  and 
'HNO3. 

Mercury,  Hg  (Hydrargyrum) . 

The  Metal.  —  Atomic  weight  200.6.  Occurs  as  red  sulphide, 
cinnabar,  and  in  small  quantities  amalgamated  with  silver  or 
gold  or  combined  with  chlorine  or  iodine.  It  is  the  only  metal 
which  is  Hquid  at  ordinary  temperatures,  sohdifying  at  —39°  C. 

The  molecule  of  mercury  consists  of  a  single  atom. 

*  The  author  uses  mimeograph  copies  of  these  experiments  with  space  for  the 
reactions  and  colors  of  precipitates,  which  are  filled  out  without  reference  to  the 
book  and  handed  in  by  the  student  at  the  close  of  the  laboratory  exercise. 

These  reactions  have  purposely  been  confined  to  such  as  may  be  applied  to  the 
process  of  analysis. 


METALS  OF  GROUP  I  21 

Properties.  —  It  boils  at  360°  C.  and  this  wide  range  of  tem- 
perature throughout  which  the  fluid  form  is  maintained,  together 
with  its  comparatively  great  coefficient  of  expansion  (about 
1/160),  makes  it  particularly  suitable  for  use  in  thermometers 
and  other  instruments  for  measuring  temperature  or  pressure. 

At  about  270°  C.  mercury  combines  with  oxygen  forming 
the  red  mercuric  oxide.  At  the  boiling  point,  it  readily  leaves 
other  metals,  with  which  it  has  combined,  making  the  purification 
by  dry  distillation  a  comparatively  simple  process.  The  redis- 
tilled and  chemically  pure  mercury  is  usually  obtained  by  dis- 
tillation in  vacuo. 

Certain  mixtures  of  metals  and  mercury  act  as  true  chemical 
compounds  forming  an  exception  to  the  foregoing  statement  re- 
garding the  separation  of  mercury  by  heat.  (See  Chapter  XIII, 
page  119.) 

Alloys  of  mercury  are  amalgams  and  will  be  considered 
under  this  head. 

Compounds.  —  Mercury  forms  two  series  of  salts;  one,  mer- 
curous,  referable  to  the  oxide  Hg20,  in  which  mercury  exhibits 
a  valence  of  one;  and  the  other,  mercuric,  referable  to  HgO, 
the  mercury  having  a  valence  of  two. 

(Mercuric  compounds  will  be  considered  under  group  two.) 

Mercurous  chloride,  or  calomel,  may  be  made  by  the  reduc- 
tion of  HgCl2  by  a  reducing  agent,  as  SO2.  2  HgCl2  +  2  H2O 
-\-  SO2  =  2  HgCl  +  H2SO4  +  2HCI;  but  the  process  commercially 
employed  is  usually  to  sublime  a  mixture  of  mercuric  sulphate, 
sodium  chloride  and  mercury. 

HgS04  +  2  NaCl  -1-  Hg  =  2  HgCl  +  Na2S04. 

Mercurous  iodide,  Hgl,  is  a  greenish  colored  unstable  salt 
produced  by  double  decomposition  of  HgNOs  and  KI. 

Mercurous  nitrate  is  an  easily  soluble  salt  produced  by  action 
of  cold  nitric  acid  on  excess  of  mercury,  a  solution  of  which  may 
be  used  for  the  study  of  mercurous  precipitates. 

Note.  —  The  solution  of  mercurous  nitrate,  upon  standing,  will  be  foimd  to 
contain  more  or  less  mercuric  nitrate,  unless  care  is  taken  to  keep  excess  of  mer- 
cury in  the  bottom  of  the  bottle. 


22      SALTS   OF   THE  METALS   AND  QUALITATIVE  ANALYSIS 

Analytical  Reactions.  —  HgNOs  with  HCl  gives  a  white 
precipitate  of  HgCl  (calomel).  After  the  precipitate  has  settled, 
decant  the  Uquid,  and  test  the  solubiKty  of  the  HgCl  in  ammonia 
water.  Does  it  dissolve?  How  does  its  behavior  differ  from 
that  of  AgCl? 

Alkahne  hydroxides  form  with  mercurous  salts  the  black 
oxide  Hg20,  a  preparation  of  which,  made  with  lime-water  and 
calomel,  is  known  as  "  black  wash." 

Lead,  Pb  (Plumbum). 

The  Metal. — Atomic  weight  207.1.  Occurs  as  sulphide 
(Galena),  PbS;  in  lesser  quantities  as  native  carbonate  (Cerus- 
site) ;  also  as  phosphate,  chromate,  and  sulphate. 

Lead  is  reduced  from  the  sulphide  in  a  reverberatory  furnace 
by  a  few  simple  reactions  as  follows:  3  PbS  +  5  O2  =  2  PbO  + 
PbS04  +  2  SO2;  then,  by  increasing  the  heat  without  access  of 
air,  the  sulphur  is  driven  off  and  the  lead  separates  by  two 
double  decompositions, 

2  PbO  +  PbS  =  3  Pb  +  SO2  and  PbS04  +  PbS  =  2  Pb  +  2  SO2. 

Properties.  —  Melting-point  from  325°  to  335°  C.  Lead  is 
one  of  the  softest  of  the  metals  and  can  be  easily  cut  with  a 
good  knife.     It  is  a  very  poor  conductor  of  electricity. 

Presence  of  small  quantities  of  antimony  or  arsenic  tend  to 
harden  the  metal.* 

Lead  is  very  easily  separated  from  its  compounds  by  reduction 
with  carbon. 

Lead  is  soluble  in  nitric  or  acetic  acid,  forming  Pb(N03)2  or 

Pb(C2H302)2. 

Lead  is  also  dissolved  to  a  very  slight  extent  by  pure  water 
containing  oxygen,  or  by  water  containing  CO2,  mineral  salts,  or 
organic  matter.  It  tarnishes  in  the  air,  with  formation  of  a 
suboxide,  Pb20. 

*  Hepburn,  page  137. 


METALS  OF  GROUP  I  23 

Alloys.  —  Lead  forms  a  large  number  of  important  alloys 
among  which  are  solders  and  fusible  metals  as  given  in  Chapter 
XI\',  and  t\-pe  metal  which  is  an  alloy  of  lead  and  antimony. 

Compounds.  —  Besides  the  suboxide  of  lead  above  mentioned, 
three  more  compounds  of  lead  and  ox^-gen  are  of  interest. 

Litharge,  PbO.  is  the  yellow  oxide  used  in  pharmacy  as  the 
base  of  **  Diacylon  plaster.  " 

The  black  oxide.  PbO;,  is  used  as  an  oxidizing  agent.     Red 
lead  (miniumX-  PbsO^,  is  practically  a  mixture  of  PbO-  and  2  PbO, 
and  used  as  a  source  of  PbO:  by  treatment  with  HXO3. 
PbsO,  +  4  HXO,  =  PbO,  -  2  Pb(X03)2  +  2  H^O. 

Lead  carbonate,  as  prepared  by  precipitation  of  soluble  lead 
salts  by  alkali  carbonates,  has  the  composition  (PbC03)2Pb(OH)a. 

The  basic  carbonate,  prepared  by  exposure  of  the  metal  to 
fumes  of  acetic  acid,  COo,  and  moisture,  is  known  as  "  white 
lead,**  and  is  used  in  manufacture  of  paint. 

Lead  acetate,  or  sugar  of  lead,  formed  by  solution  of  the 
metal  or  the  oxide,  PbO,  in  acetic  acid,  is  a  white  soluble  salt 
crj-stallizing  with  three  molecules  of  H.O.  The  solution  has  an 
acid  reaction  to  Ktmus  paper. 

Lead  subacetate,  or  basic  acetate  of  leadj  a  solution  of  which 
is  known  as  Goulard's  extract,*  is  made  by  boiling  lead  acetate 
solution  with  litharge.  It  is  used  in  medicine  as  an  external  ap- 
plication and  in  physiological  chemistr}-  as  a  reagent.  It  deteri- 
orates by  absorption  of  CO2  and  precipitation  of  a  carbonate. 

Lead  chromate  (chrome  yellow)  is  a  yellow  insoluble  salt  used 
as  a  pigment. 

Lead  nitrate,  an  easily  soluble  white  cr}-staUine  salt,  may  be 
used  in  the  study  of  the  analytical  reactions  of  lead. 

Lead  arsenate,  a  poisonous  salt,  is  quite  largely  used  for 
spraying  trees. 

Analytical  Reactions.  —  Pb  XO.3 '2  with  2  HCl  gives  white  pre- 
cipitate of  PbCL.    Test  its  solubility  in  hot  water  and  in  XH4OH. 

*  Preparation  on  page  ^jS  . 


24      SALTS   OF    THE   METALS   AND  QUALITATIVE   ANALYSIS 

Pb(N03)2  with  NH4OH  gives  white  precipitate  of  Pb(0H)2 
insoluble  in  hot  water. 

Pb(N03)2  with  HoS  gives  black  PbS.  Test  solubility  of 
precipitate  in  warm  dilute  HNO3. 

Pb(N03)2  with  H2SO4  gives  white  precipitate  of  PbS04,  form- 
ing slowly  in  dilute  solutions. 

Pb(N03)2  with  K2Cr04  (or  K2Cr.207)  gives  a  yellow  pre- 
cipitate of  PbCr04. 

Pb(N03)2  gives  with  KI  a  yellow  precipitate,  PbL.  Avoid 
excess  of  the  potassium  iodide. 

By  application  of  the  reactions  of  the  salts  of  Ag,  Pb,  and 
Hg',  we  may  formulate  a  scheme  for  the  separation  and  identi- 
fication of  the  metals  of  Group  I  as  follows: 

Analysis  of  Group  I. 

(Ag,  Pb,  Hg'.) 

To  the  clear  solution  to  be  tested  add  slowly  dilute  HCl  as 
long  as  any  precipitation  occurs.  Filter  and  wash  the  precipi- 
tate once  with  cold  water,  add  this  washing  to  filtrate  to  be 
tested  for  remaining  groups,  then  wash  precipitate  on  the  paper 
with  several  small  portions  of  Jiot  water. 


AkCI  and  HgCl  remain  undissolved. 


PbCl'.  is  in  llie  liot-water  solution. 


^ 


Divide  this  hot-water  solution  into  three  parts  and  make 
three  of  the  following  tests  for  lead:  First,  with  K2Cr207,  which 
gives  yellow  precipitate  of  PbCr04.  Second,  with  dilute  H2SO4, 
giving  a  white  precipitate  of  PbS04.  Third,  with  H2S  water, 
giving  black  precipitate  of  PbS.  Fourth,  with  KI  solution,  which 
forms  a  yellow  precipitate  of  Pbl2.     Write  these  reactions. 


METALS  OF  GROUP  I 


25 


To  undissolved  residues  of  Hg  and  Ag  chlorides  add  warm 
NH4OH. 


Hg  remains  on  the  paper,  black,  as  Hg  +  NH2HgCl. 

Ag  is  dissolved  by  the  NH4OH  and  may  be  precipitated 
as  AgCl  by  adding  HNO3  to  acid  reaction.  Presence  of 
Hg  in  the  blacii  residue  may  be  confirmed  as  in  Group  II 

(page  48). 


OUTLINE   SCHEME  FOR  ANALYSIS   OF   GROUP  I. 

To  about  one-third  of  a  test-tubeful  of  the  unknown  solution  add  a  few  drops 

of  HCl. 

Ppt.  =  AgCl,  HgCl,  PbCl2.     Filter,  add  hot  H2O. 


Residue  =  AgCl,  HgCl. 
Add  NH4OH. 


Residue  =  HgCl. 
Test,  as  above. 


Solution  =  AgCl. 
Test  with  HNO3. 


Solution  =  PbCU. 
Test  as  on  page  24. 


QUESTIONS  ON  GROUP  I. 

Why  wash  the  precipitated  chlorides  only  once  with  cold 
water? 

Why  is  it  necessary  to  wash  the  lead  chloride  out  with  hot 
water  before  using  ammonia? 

Why  is  ammonia  used? 

How  does  nitric  acid  reprecipitate  silver  chloride? 

WTiy  is  it  necessary  to  use  two  or  more  confirmatory  tests 
for  the  presence  of  lead? 

What  other  metal  in  group  one  would  give  a  black  precipi- 
tate with  hydrogen  sulphide  water? 

What  precaution  must  be  used  in  testing  for  soluble  salts  of 
lead  with  potassium  iodide? 


CHAPTER   IV. 
METALS   OF   GROUP   H. 

Copper,  Cu  (Cuprum). 

The  Metal.  —  Atomic  weight  63.57.  Occurs  free  in  vicinity 
of  Lake  Superior;  also  in  western  United  States,  ChiH,  and  Spain, 
as  sulphides,  copper  pyrites,  chalcopyrite,  CuFeS^;  and  copper 
glance,  chalcocite,  CU2S.  Malachite  green  and  malachite  blue 
are  native  basic  carbonates  of  copper. 

Properties.  —  Melting  point  1084°  C.  Copper  dissolves 
easily  in  nitric  acid  and  with  difficulty  in  hydrochloric  acid; 
heated  with  sulphuric  acid  it  forms  copper  sulphate,  with  the 
evolution  of  sulphur  dioxide.  Copper  is  second  to  silver  as  a 
conductor  of  heat  and  electricity.  It  expands  sHghtly  on  solidi- 
fying and  is  corroded  by  carbon  dioxide  and  moisture  forming  a 
green  carbonate. 

Alloys.  —  The  alloy  wdth  mercury,  amalgam,  was*  formerly 
used  in  dentistry  to  a  considerable  extent  (page  122).  Copper 
alloys  in  all  proportions  with  gold,  silver,  nickel,  and  zinc.  It 
hardens  silver  and  gold,  and  is  used  in  the  manufacture  of  coins, 
jewelry  and  the  solders  used  in  crown  and  bridge  work.  Copper 
is  also  used  in  the  preparation  of  bronze,  brass,  bell  metal,  den- 
tal gold,  German  silver,  Mannheim  gold.  Mosaic  gold,  Dutch 
metal,  and  Aich's  metal.  For  composition  of  copper  alloys,  see 
page  114. 

Compounds.  —  Salts  and  solutions  of  copper  are  usually  blue 
or  green.  Copper  forms  two  series  of  salts:  the  cuprous,  of 
which  there  are  but  few  important  examples,  and  the  cupric. 
Cuprous  oxide,  CU2O,  which  is  red  in  color  (sometimes  yellow 

26 


METALS  OF  GROUP  II  27 

through  admLxturc  of  cuprous  hydroxide)  is  obtained  by  reduc- 
tion of  cupric  salts  by  organic  substances  such  as  sugar.  Cu- 
prous chloride  is  used  as  a  reagent  for  the  detection  of  acetylene 
gas.  Cuprous  iodide  is  a  white,  insoluble  powder  used  in  the 
preparation  of  the  white  copper  cements.     (See  page  138.) 

Cupric  oxide,  CuO,  is  a  black  powder  formed  by  ignition  of 
copper  in  the  air  or  by  boihng  copper  solution  with  the  fLxed 
alkali  hydroxides. 

Copper  arsenate  and  aceto-arsenite,  the  latter  known  as 
Paris  green,  are  both  green  powders  which  have  been  used  as 
pigments  and  as  insecticides. 

Copper  sulphate,  CUSO4,  crystallizes  with  five  moleciiles  of 
water  and  is  known  as  bluestone  or  blue  \'itriol.  It  is  used  ex- 
tensively in  the  "  Gra\'ity  battery,"  and  in  copper  plating. 

Verdigris  is  a  sub-acetate  or  oxy-acetate  of  copper;  composi- 
tion, CU20(C2H302)2. 

Copper  salts  combine  with  amimonia,  forming  a  series  of 
"  cuprammonium  ''  compounds  freely  soluble  and  of  intense 
blue  color. 

The  chloride  nitrate  and  sulphate  are  the  common  soluble 
salts.  A  1 5c  solution  of  either  of  these  will  give  the  analytical 
reactions. 

Analytical  Reactions. — CuSO^  withH2S  gives  CuS,  a  brownish- 
black  sulphide.  Test  its  solubility  in  (XH4)2S  and  in  warm 
dilute  XHO3. 

CuSOi  with  NH4OH  (one  or  two  drops  of  reagent)  will  pre- 
cipitate Cu(0H)2,  bluish  white.  x\dd  more  NH4OH  to  the  same 
test-tube  and  note  the  result.  To  tliis  clear  solution  add  a 
sufficient  amount  of  dry  KCX  to  completely  decolorize  the  liquid. 
Then  add  to  the  mixture  some  H2S  water.  Is  the  black  CuS 
thrown  out?  The  beha\ior  of  Cu  solutions  thus  treated  is  due 
to  the  formation  of  double  salts,  the  solution  in  ammonia  being 
due  to  a  compound  of  CUSO4  and  NH3,  and  the  decolorization 
of  the  blue  solution  to  one  of  Cu(CN)2  and  KCN. 


28    SALTS   OF   THE  METALS  AND  QUALITATIVE  ANALYSIS 

CUSO4  with  K4FeCy6  (potassium  ferrocyanide)  gives  in  acetic 
acid  solution  a  red-brown  precipitate  of  Cu2FeCy6. 

Metallic  zinc  or  iron  will  precipitate  copper  from  solution. 
Hold  a  knife-blade  in  a  solution  of  CUSO4  for  a  few  seconds. 

Mercury  in  Mercuric  Combination. 

Compounds  of  Dyad  Mercury.  —  Mercuric  oxide,  HgO,  is 
a  red  powder  obtained  by  ignition  of  mercury  in  the  air.  Mer- 
curic oxide  may  also  be  prepared  by  precipitation  of  mercuric 
chloride  with  alkaline  hydroxides.  The  oxide  thus  formed  is 
yellow  in  color,  and,  when  prepared  by  mixing  mercuric  chloride 
and  lime  water,  forms  the  "  yellow  wash  ''  used  to  a  considerable 
extent  in  pharmacy. 

Mercuric  chloride,  HgCla.  This  intensely  poisonous  salt  is 
known  by  the  fairly  descriptive  name  of  corrosive  sublimate. 
It  corrodes  metals,  such  as  zinc  and  iron;  it  coagulates  albumin 
and  acts  as  a  corrosive  poison  when  taken  internally. 

It  is  made  in  a  manner  analogous  to  that  used  for  the  prepa- 
ration of  calomel,  i.e.,  by  sublimation,  the  salts  used  in  this 
instance  being  mercuric  sulphate  and  sodium  chloride  alone. 
HgS04  -\-  2  NaCl  =  HgClo  -1-  Na2S04. 

Mercuric  chloride  is  antiseptic  and  a  disinfectant  in  dilu- 
tions of  one  to  a  thousand.  Antiseptic  tablets  designed  to  give 
about  this  strength  of  solution  by  the  addition  of  one  tablet  to 
one  pint  of  water  are  made  to  contain  7.7  grains  HgCl2  and  7.3 
grains  NH4CI,  with  sufficient  purple  coloring  to  advertise  the 
nature  of  the  tablets  and  thus  act  as  a  safeguard  against  acci- 
dental poisoning.  Mercuric  chloride  is  soluble  in  water  and  in 
alcohol.  It  is  used  in  the  preparation  of  antiseptic  gauze,  sterile 
cotton,  etc.,  but,  on  account  of  its  corrosive  properties,  cannot 
be  used  to  sterilize  instruments. 

Ammoniated  mercury,  mercur-ammonium  chloride  or  white 
precipitate  (NH2HgCl)  is  a  white  powder  obtained  by  slowly 
pouring  a  solution  of  HgCl2  into  ammonia  water. 


METALS  OF  GROUP  II  29 

Mercuric  iodide,  red  iodide  (Hgl>),  is  made  by  reaction  of 
mercuric  chloride  with  potassium  iodide: 

HgClo  +  2  KI  =  2  KCl  +  Hgl2. 

Mercuric  iodide  is  soluble  in  excess  of  either  reagent,  also  in 
alcohol. 

]\Iercuric  iodide  combines  with  potassium  iodide  (KI)  form- 
ing an  iodo-hydrargyrate,  used  as  a  reagent  in  physiological 
chemistry  (page  406),  also  as  an  alkaloidal  precipitant. 

_An  alkaline  solution  of  potassium  iodo-hydrargyrate  con- 
stitutes Nessler's  reagent,  used  in  analysis  of  water  and  of  saliva 
as  a  test  for  ammonium  compounds. 

Analytical  Reactions.  —  A  2%  solution  of  corrosive  sub- 
Hmate  (HgCl2)  may  be  used  in  demonstrating  the  reactions  of 
dyad  mercury. 

HgCb  with  HoS  gives  first  a  white  precipitate,  turning  yellow, 
brown,  and  finally  black,  as  proportion  of  HoS  increases.  The 
black  precipitate  oiily  is  mercuric  sulphide,  and  care  must  be 
taken  to  add  H2S  till  this  compound  is  produced. 

Test  the  solubiHty  of  HgS  in  (NH4)2S  and  HNO3. 

To  HgClo  solution  add  SnCb.  The  mercuric  chloride  is 
reduced  to  mercurous  chloride  (HgCl,  white)  or  metallic  mercury 
(Hg,  gray),  according  to  proportions  used: 

2  HgClo  +  SnClo  =  2  HgCl  +  SnCl4, 

or  Hga2  +  SnCb  =Hg-\-  SnCU. 

HgCl2  mth  KI  gives  red  IIgl2,  easily  soluble  in  excess  of 
either  of  the  reagents. 

HgCl2  with  NH4OH  gives  white  precipitate  of  (NH2Hg)Cl, 
known  as  "  white  precipitate "  (see  ammoniated  mercury). 
"  Red  precipitate  "  is  a  term  sometimes  used  to  designate  the 
red  oxide  of  mercury,  HgO,  made  in  the  dry  way. 


30    SALTS  OF   THE  METALS   AXD  QUALITATIVE  ANALYSIS 

Bismuth,  Bi. 

The  Metal.  —  Atomic  weight  208.  Bismuth  does  not  occur 
in  large  quantities,  but  is  usually  found  in  the  free  state.  Small 
amounts  are  obtained  from  the  oxide,  Bi203,  bismuth  ochre,  and 
from  the  sulphide,  BioSs. 

It  is  easily  identified  by  means  of  the  blo\\'pipe  test  on  plaster 
with  S  and  KI  (page  128). 

Properties.  —  Melting-point  268^  C.  It  is  a  crystalline 
metal,  expands  upon  cooling  and  readily  unites  with  oxygen 
burning  with  a  bluish  flame  to  bismuth  oxide.  At  ordinary 
temperatures  it  is  brittle  and  readily  dissolved  by  nitric  acid. 

Alloys.  —  The  most  important  alloys  from  a  dental  stand- 
point are  the  fusible  metals,  Melotte's  metal,  Wood's  metal, 
Rose's  metal,  Newton's  alloy,  etc.  (page  128). 

Fletcher  states  that  an  amalgam  \\dth  one  part  bismuth, 
fifteen  parts  tin,  and  fifteen  parts  silver,  filed  and  amalgamated 
with  four  parts  of  mercury  to  one  part  of  the  alloy,  will  adhere 
to  a  flat  dry  surface  and  may  be  used  as  a  metallic  cement  upon 
apparatus,  giving  an  air-tight  joint  of  great  strength. 

Compounds.  —  Salts  of  bismuth  as  a  rule  require  excess  of 
acid  for  permanent  solution;  and,  by  adding  a  considerable  vol- 
ume of  water  they  are  easily  thrown  out  of  solution  as  insoluble 
basic  or  oxysalts,  the  reaction  of  the  nitrate  being  as  follows: 

Bi(N03)3  +  H2O  =  BiON03  +  2  HXO3. 

This  may  be  demonstrated  by  allowing  a  few  drops  of  bis- 
muth solution  to  fall  into  a  comparatively  large  amount  of  water 
(two  to  six  ounces) .  A  white  cloud  of  insoluble  oxysalt  may  be 
observed  settling  through  clear  water.  This  may  be  employed 
as  a  final  test  for  bismuth  in  the  course  of  systematic  analysis. 

The  subnitrate  and  the  subcarbonate  of  bismuth  are  both  used 
in  medicine.  The  latter  is  a  common  starting-point  in  the 
preparation  of  other  bismuth  salts. 


METALS  OF  GROUP  II  31 

Analjrtical  Reactions.  —  The  most  available  salt  is  the  ni- 
trate, insoluble  in  water  unless  strongly  acidulated. 

Use  a  2%  solution  of  Bi(N03)3  in  the  follo^^dng  tests: 

Bi(N03)3  "tvdth  NH4OH  gives  white  precipitate  of  bismuth 
hydroxide  Bi(0H)3. 

Bi(X03)3  "W'ith  HoS  precipitates  BioSs,  brownish  black,  in- 
soluble in  (NIIi)2S,  but  soluble  in  warm  dilute  HNO3. 

Bi(0H)3  reacts  with  sodium  stannite  (prepared  by  adding 
NaOH  to  SnClo  till  precipitate  dissolves)  gi^'ing  a  black  precipi- 
tate of  metallic  bismuth. 

4  NaOH  -\-  SnCl2  =  NaoSnO.  -f-  2  NaCl  +  2  HoO. 
2  Bi  (0H)3  +  3  Na2Sn02  =  2  Bi  4-  3  NaaSnOa  +  3  H2O. 


Cadmujm,  Cd. 

The  Metal.  —  Atomic  weight  11 2. 4.  Occurs  associated  with 
zinc  in  zinc  blende.  It  is  more  easily  volatile  than  zinc,  and 
advantage  is  taken  of  this  fact  in  effecting  its  separation  from 
that  metal. 

Properties.  —  Melting-point  332°  C.  Cadmium  is  a  com- 
paratively soft  metal  though  harder  than  zinc  or  tin.  It  is  usu- 
ally found  in  trade  in  the  form  of  rods  which  crackle  somewhat 
like  tin  when  bent. 

It  dissolves  slowly  in  sulphuric  acid  or  hydrochloric  acid  mth 
the  evolution  of  hydrogen,  and  easily  in  nitric  acid  with  the  pro- 
duction of  nitrogen  oxides.  It  is  also  soluble  in  solution  of 
ammonium  nitrate,  forming  cadmium  nitrite  and  ammonium 
nitrite. 

Alloys.  —  Cadmium  is  used  as  a  constituent  of  fusible  metals 
and  rarely,  in  small  proportion,  in  dental  aUoys.  Its  use  in 
the  latter  case  is  objectionable  on  account  of  the  production  of 
yellow  stain  of  cadmium  sulphide  which  penetrates  the  dentine 
(page  123). 


32      SALTS  OF   THE  METALS  AND  QUALITATIVE  ANALYSIS 

Analytical  Reactions.  —  A  2%  solution  of  the  sulphate  or 
nitrate  may  be  used  in  studying  the  deportment  of  cadmium 
salts. 

CdS04  with  H2S  gives  a  bright  yellow  sulphide,  CdS,  soluble 
in  dilute  nitric  acid. 

CdS04  with  (NH4)2S  also  precipitates  the  yellow  sulphide. 

Cadmium  sulphide  forms  slowly,  and,  in  presence  of  Cu  or 
other  second-group  metals,  may  escape  precipitation  if  the  re- 
agent is  added  in  insufficient  quantity. 

Arsenic,  As. 

The  Element.  —  Atomic  weight  75.0.  Arsenic  is  on  the 
borderline  between  the  metallic  and  non-metallic  elements,  its 
acid-forming  properties  predominating.  It  occurs  associated 
with  copper  and  iron  sulphides,  as  arsenical  pyrites,  FeAs.FeS2; 
as  native  sulphides,  orpiment,  AS2S3,  and  realgar,  AS2S2;  also 
to  some  extent  as  the  trioxide,  AS2O3. 

Compounds.  —  Arsenic  forms  two  series  of  salts,  the  ar- 
senious,  As"^,  and  arsenic,  As"^,  and  it  also  acts  as  an  acid  radical 
forming  arsenious  and  arsenic  acids.  In  the  process  of  analysis, 
arsenic  compounds  whether  acid  or  basic  are  reduced  to  arseni- 
ous by  action  of  hydrogen  sulphide.  It  is  most  easily  obtained 
in  the  form  of  the  trioxide,  AS2O3,  also  known  as  arsenious  acid 
or  white  arsenic. 

White  arsenic  is  intensely  poisonous;  but,  nevertheless,  it 
has  been  very  freely  used  in  curing  the  skin  of  fur-bearing  animals 
and  otherwise  as  a  preservative.  In  dentistry  white  arsenic  is 
used  to  devitalize  pulp. 

Arsenic  is  widely  distributed  in  nature.  It  occurs  in  soft 
coal  from  which  source  it  finds  its  way  into  the  roadside  dust 
and  any  substance  capable  of  holding  dust,  such  as  the  majority 
of  fabrics,  wall  papers,  etc.  Arsenic  is  a  common  impurity  in 
mercury,  zinc,  and  commercial  acids.  Inasmuch  as  these  things 
are  largely  used  in  the  preparation  of  amalgam  and  cement 


METALS  OF  GROUP  II  33 

fillings,  it  is  necessary  that  considerable  pains  be  taken  to  pre- 
vent the  presence  of  the  poison  in  sufi&cient  quantity  to  cause 
irritation. 

The  poisonous  character  of  arsenic  differs  greatly  with  the 
combination  in  which  it  occurs.  A  gaseous  hydride  of  arsenic, 
AsHs,  being  among  the  most  poisonous  of  its  compounds,  while 
some  of  the  organic  compounds  are  claimed  to  be  non-poisonous. 

Arsenic  forms  an  insoluble  arsenate  with  ferric  hydrate; 
hence,  freshly  precipitated  ferric  hydroxide  is  the  official  anti- 
dote for  arsenical  poisoning.  This  is  prepared  by  mixing  150  c.c. 
of  dilute  ferric  sulphate  solution  (containing  50  c.c.  of  the  U.S.P. 
"  Solution")  with  a  well-shaken  mixture  of  10  grains  of  oxide 
of  magnesium  in  about  750  c.c.  of  water: 

Fe2(S04)3  +  3  Mg(0H)2  =  Fe2(OH)6  +  sMgSO^. 

Fowler's  solution  containing  1%  AS2O3  dissolved  by  use  of 
potassium  bicarbonate;  a  solution  of  arsenious  acid  containing 
1%  AS2O3  dissolved  by  aid  of  two  parts  of  HCl;  Donovan's 
solution  containing  1%  each  of  Asis  and  Hgl2;  and  Pearson's 
solution  containing  1%  sodium  arsenate  are  Pharmacopoeial 
preparations  of  arsenic. 

Analytical  Reactions.  —  A  solution  for  studying  the  reactions 
of  arsenic  (As™)  is  conveniently  made  by  dissolving  about  15 
grams  of  white  arsenic  in  dilute  NaOH  solution  by  aid  of  heat, 
then  diluting  to  one  liter  and  acidifying  slightly  with  HCl. 

To  an  arsenious  solution,  which  may  be  represented  by  AsCla, 
add  H2S  water.  A  lemon-yellow  precipitate  of  AS2S3  will  be 
thrown  down.  Test  the  solubility  of  this  precipitate  in  yellow 
ammonium  sulphide  and  in  ammonium  carbonate. 

To  the  alkahne  solution  of  the  sulphide  add  excess  of  HCl; 
A&2S3  is  precipitated. 

To  an  arsenious  solution  add  (NH4)2S  in  repeated  small 
portions. 

In  neutral  solution,  as  of  sodium  arsenite,  NasAsOs,  silver 


34      SALTS  OF   THE  METALS  AND  QUALITATIVE  ANALYSIS 

Iiitrate  will  throw  down  yellow  silver  arsenite,  soluble  in  excess  of 
nitric  acid  or  ammonia. 

SPECIAL   TESTS    FOR   ARSENIC. 

Reinsch's  Test  for  arsenic,  applicable  to  any  solution 
whether  organic  or  not,  and  very  valuable  for  a  prehminary  test, 
is  made  as  follows:  place  the  solution  or  mixture  to  be  tested  in 
a  porcelain  dish,  acidify  strongly  with  hydrochloric  acid,  add  a 
small  strip  of  bright  copper  foil  (cleaned  in  dilute  nitric  acid  and 
thoroughly  washed  in  distilled  water)  and  boil  for  ten  or  twenty 
minutes,  adding  sufhcient  water  to  replace  loss  by  evaporation. 
Remove  the  copper  foil ;  a  dark  gray  to  black  coating  is  an  indi- 
cation of  arsenic  but  not  conclusive,  as  some  other  substances, 
mercury  and  antimony  in  particular,  give  similar  deposits. 

To  prove  the  presence  of  arsenic,  roll  the  foil  as  tightly  as 
possible  and  place  it  in  the  bulb  of  a  small  glass  matrass  (Fig.  i). 


Fig.  I. 

Heat  the  bulb  over  a  very  small  luminous  flame,  when  tetra- 
hedral  or  octahedral  crystals  of  arsenious  trioxide  (As^Os)  will  de- 
posit in  the  constricted  portion  of  the  tube.  These  may  be  iden- 
tified by  microscopical  examination.  There  will  be  sufficient  air 
in  the  matrass  for  the  formation  of  the  oxide  and  the  test  becomes 
much  more  deUcate  than  if  heated  in  the  ordinary  open  tube  as 
often  recommended. 

Gutzeit's  Test  is  made  by  placing  the  suspected  solution 
in  a  test-tube,  acidifying  with  sulphuric  acid,  adding  a  few  small 
pieces  of  arsenic-free  zinc,  and,  as  hydrogen  begins  to  be  given  off, 
placing  over  the  mouth  of  the  tube  a  piece  of  filter-paper  carry- 
ing a  drop  of  a  strong  solution  of  silver  nitrate.  The  presence 
of  arsenic  is  indicated  by  the  darkening  of  the  moistened  filter- 
paper  in  accordance  with  the  following  reactions: 


METALS   OF  GROUP  II 


35 


The  nascent  hydrogen,  Hberated  by  action  of  the  zinc  upon 
the  acid,  forms  with  any  arsenic  present  the  gaseous  arsenious 
hydride  which,  in  contact  with  the  filter-paper  wet  with  silver 
nitrate  solution,  produces  a  brown  or  black  stain  of  metalHc 
silver,  while  the  arsenic  becomes  arsenious  acid,  H3ASO3.  The 
stain  may  possibly  be  yellow  by  formation  of  a  compound  of 
silver  arsenide  and  silver  nitrate,  but,  as  a  rule,  moisture  is 
present  in  sufficient  amount  to  insure  the  decomposition  of  this 
compound. 

Antimony  will  give  a  similar  brown  or  black  stain  (not 
yellow),  but  the  presence  of  arsenic  may  be  conclusively  demon- 
strated by  making  Fleitml^nn's  Test,  which  is  conducted  in 
the  same  way  as  the  preceding,  except  that  the  hydrogen  is 
evolved  in  alkaline  solution,  either  by  means  of  zinc  and  strong 
potassium  hydroxide  solution  (Zn  +  2  KOH  =  K2Zn02  +  H2) 
or  by  sodium  amalgam  (made  with  arsenic-free  mercury)  and 
water  (NaHg^  +  HoO  =  NaOH  +  Hg  -^  H).  In  this  case  the 
antimony  hydride  is  Jiot  formed  ;  so  a  stain  thus  obtained  con- 
stitutes a  positive  test  for  arsenic. 

Marsh's  Test  for  arsenic  (or  antimony) 
consists  of  a  simple  hydrogen  generator  with 
glass  tip  for  burning  the  gas,  as  shown  in  Fig.  2 . 
In  this  apparatus  antimony  and  arsenic  are 
converted  into  the  gaseous  hydrides,  arsenic 
hydride,  and  antimony  hydride ;  and  if  a  piece 
of  cold  porcelain  is  pressed  down  upon  the 
flame,  arsenic  or  antimony  will  be  deposited 
as  metaUic  stains  (mirrors)  upon  the  porcelain. 
^  Traces  of  antimony  may  be  retained  in  the 
generator  by  the  introduction  of. a  piece  of 
platinum-foil,  the  antimony  being  precipitated 
upon  the  platinum  to  which  it  adheres  quite  strongly. 

To  distinguish  between  arsenic  and  antimony  spots  the  follow- 
ing tests  will  suffice: 


Fig.  2. 


36      SALTS  OF   THE   METALS  AND  QUALITATIVE   ANALYSIS 


Arsenic. 
Brown-black,  lustrous  spots. 
Soluble  in  solution  of  hypochlorite  of 

lime  or  soda. 
Easily  volatilized. 


Antimony. 
Dead  brown  or  black  surfaces. 
Insoluble  in  solution  of  hypochlorite  of 

lime  or  soda. 
Volatilized  at  red  heat. 


The  Marsh-Berzelius  Test  for  arsenic  is  the  most  delicate 
of  all  and  the  one  to  which  we  resort  in  detecting  arsenic  in  the 
saliva  or  the  urine.  By  this  method  one  two-hundredth  of  a 
milligram  or  about  1/12800  of  a  grain  can  be  easily  shown  as  a 
brown  deposit  in  the  constricted  tube  at  about  the  point  K,  Fig.  3. 


Fig.  3. 

The  apparatus  used  in  this  test  is  shown  in  Fig.  3,  and  consists 
of  a  small  Erlenmeyer  flask,  or  wide-mouth  bottle,  fitted  as  a 
hydrogen  generator.  A,  and  connected  with  a  drying-tube,  B, 
filled  with  fused  calcium  chloride,  then  with  a  tube  of  hard  glass, 
C,  drawn  out  to  a  very  small  diameter  for  half  its  length. 

The  generator  A  is  charged  with  arsenic-free  zinc,  and  dilute 
sulphuric  acid  (1/5)  introduced  through  the  thistle-tube  E. 
After  all  air  has  been  driven  from  the  apparatus,  Hght  the  escaping 
hydrogen  at  T,  then  the  Bunsen  burner  D,  and  allow  the  gen- 


METALS  OF  GROUP  II 


37 


erator  to  run  for  about  twenty  minutes,  thus  making  a  blank 
test  of  apparatus  and  reagents;  if  at  the  end  of  this  time  the 
hard  glass  is  perfectly  free  from  any  deposit  the  suspected  liquid, 
which  must  have  been  freed  from  organic  matter  (process  de- 
scribed in  detail  in  chapter  on  Urine  Analysis),  may  be  introduced 
in  portions  of  about  lo  c.c.  each. 

The  flame  should  be  spread  somewhat  so  as  to  heat  at  least 
one  inch  of  the  glass  tube.  This  may  be  ac- 
complished, in  the  absence  of  a  burner-tip, 
b}'  placing  an  inverted  V-shaped  piece  of  as- 
bestos board,  one  inch  wide,  over  the  heated 
part  of  the  tube. 

The  presence  of  arsenic  increases  the  evo- 
lution of  hydrogen  and,  unless  the  solution 
is  added  gradually,  the  arsenious  hydride 
may  be  driven  so  rapidly  past  the  flame  as 
to  escape  decomposition,  or  the  tube  may 
become  heated  to  such  an  extent  that  arsenic 
will  not  be  deposited. 

The  escape  of  arsenic  at  T  may  be 
noticed  by  the  bluish  color  of  the  flame 
and  by  the  characteristic  garlic  odor. 

Antimony  is  similarly  deposited  as  a 
dead-black  stain  instead  of  brown-black, 
and  as  antimony  is  less  easily  volatile 
than  arsenic  the  deposit  will  be  nearer 
the  flame,  possibly  on  both  sides  of  it. 

Mercuric  Bromide  Test.  —  Sanger  and 
Black*  have  modified  the  Gutzeit  test 
making  the  determination  of  arsenic  a  quantitative  one  as 
follows:  The  arsenious  hydride  is  passed  through  a  drying  tube 
containing  filter-paper  (in  bulb.  Fig.  4)  wet  with  lead  acetate 

*  Proceedings  of  the  American  Academy  of  Arts  and  Sciences,  Vol.  XLIII, 
No.  8,  October  1907. 


38      SALTS   OF   THE   METALS  AND  QUALITATIVE   ANALYSIS 

solution  to  absorb  sulphur  compounds.  Then  the  gas  is  passed 
through  absorbent  cotton  in  upper  part  of  drying  tube,  and  then 
over  a  paper  moistened  with  mercuric  chloride  (small  tube  above 
drying  tube)  when  the  arsenic  produces  a  yellow  to  brown  color 
on  the  strip  of  hlter-paper. 

The  deUcacy  of  this  test  may  be  increased  by  using  mercuric 
bromide  in  place  of  mercuric  chloride.  The  process  has  the 
advantage  of  being  independent  of  heat  and  consequent  danger 
of  exploding  any  mixture  of  hydrogen  and  air.  The  HgBr2  paper 
is  stained  yellow  to  brown  beginning  at  the  end  next  to  the 
generator,  and  by  carefully  regulating  conditions  the  extent  of 
the  stain  may  have  a  quantitative  value. 

Arsenic  compounds  (As^),  as  Na2HAs04,  are  of  but  little 
interest  from  the  dentist's  standpoint. 

All  arsenic  compounds  are  reduced  by  nascent  hydrogen  to 
arsenious  combinations,  then  to  elementary  arsenic,  then  to 
arsine,  (AsHs),  hence  the  special  tests  given  for  arsenious  com- 
pounds are  applicable. 

Free  chlorine,  nitric  acid,  and  potassium  ferricyanide  oxidize 
arsenious  compounds  to  arsenic,  and  in  this  condition  the  ar- 
senic is  not  easily  volatihzed  and  organic  matter  may  be  destroyed 
by  deflagration  (in  presence  of  excess  of  nitrates)  with  but  slight 
loss  of  arsenic. 

Antimony,  Sb  (Stibium). 

The  Metal.  —  Atomic  weight  120.2.  Occurs  native  in  Aus- 
tralia, and  as  the  sulphide  Sb2S3,  known  as  stibnite  or  antimo- 
nite  from  which  it  may  be  easily  reduced  by  heating  \vith 
metalKc  iron  according  to  the  following  reaction: 

Sb2S3  -f  3  Fe  =  Sb2  -f  3  FeS. 

Properties.  —  Brittle  crystalhne  substance  volatile  at  high 
heat.  It  ultimately  burns  to  antimonious  oxide  (Sb203).  Sol- 
uble with  difficulty  in  sulphuric  or  hydrochloric  acids. 


METALS  OF  GROUP  II  39 

With  nitric  acid,  antimony  acts  in  a  similar  manner  to  tin, 
forming  an  oxide  which  may  be  antimonious  (Sb203)  or  anti- 
monic  (Sb205)  according  to  quantity  and  concentration  of  acid 
used  (Prescott  &  Johnson). 

Alloys.  —  Antimony  is  used  in  making  type  metal,  Britarmia 
metal,  and  rarely  in  low-grade  dental  alloys. 

Compounds.  —  The  salts  of  antimony  may  be  classified  as 
antimony  salts,  referable  to  the  hydroxide  Sb(0H)3,  and  anti- 
monyl  salts,  referable  to  SbO(OH). 

Butter  of  antimony,  antimony  trichloride,  SbCls,  when  pure, 
is  a  colorless  solid  of  buttery  consistency,  hence  its  name.  It 
may  be  formed  by  direct  union  of  constituent  elements. 

Salts  of  antimony  tend  to  form  oxycompounds  and  are  held 
in  solution  by  excess  of  acid.  The  antimonious  chloride  SbClg, 
in  solution  with  hydrochloric  acid  is  precipitated  by  excess  of 
water  as  a  white  oxychloride  Sb4Cl205,  also  known  as  "  powder 
of  Algaroth. ' '  The  antimonic  chloride  in  Hke  manner  precipitates 
the  antimonic  oxychloride,  SbOCls.  Demonstrate  by  turning 
I  or  2  c.c.  of  SbCls  solution  into  a  large  excess  of  water. 

Tartar  emetic,  K(SbO)C4H406,  may  be  prepared  by  boiling 
antimony  oxide  and  bitartrate  of  potassium,  filtering  and  allow- 
ing the  hot  solution  to  crystalUze.  It  crystallizes  with  one-half 
molecule  of  water. 

Analjrtical  Reactions.  —  A  2%  aqueous  solution  of  tartar 
emetic  may  be  used  in  the  following  tests : 

To  an  antimony  solution  represented  by  SbCls  add  H2S 
water:  Sb2S3  is  precipitated  orange-red.  Test  solubiHty  of  the 
precipitate  in  (NH4)2S  and  in  (NH4)2C03. 

How  does  it  differ  from  arsenic? 

Upon  the  addition  of  HChiri  excess  to  the  ammonium  sul- 
phide solution  the  Sb  is  reprecipitated,  but  not  necessarily,  as 
Sb2S3,  but  more  usually  as  Sb2S5  or  a  mixture  of  the  two  sulphides. 


40      SALTS  OF    THE   METALS   AND  QUALITATIVE  ANALYSIS 

Tin,  Sn  (Stannum). 

The  Metal.  —  Atomic  weight  119.  Cassiterite,  or  tin-stone, 
nearly  pure  stannic  oxide  (SnOa),  is  by  far  the  most  important 
source.     The  free  metal  has  been  found  associated  with  gold. 

Banca  tin  from  the  East  Indies  and  block  tin  from  England 
are  pure  varieties  of  the  commercial  article, 

Properties.  —  Pure  tin  will  give  a  peculiar  crackling  sound 
when  bent,  due  to  the  crystalline  structure  of  the  metal.  Tin 
is  very  malleable  at  the  ordinary  temperature,  being  fifth 
in  the  Hst  of  malleable  metals  (see  page  in),  but  becomes 
brittle  when  heated  to  about  200°  C. 

Hydrochloric  acid  dissolves  tin  slowly,  forming  stannous 
or  stannic  chlorides  according  to  the  proportion  and  temperature 
of  the  acid  used. 

Cold  dilute  nitric  acid  will  dissolve  tin,  forming  stannous 
nitrate. 

Metallic  tin  is  not  dissolved  by  strong  nitric  acid,  but  is 
converted  into  a  white,  insoluble  metastannic  acid.  Hot  dilute 
nitric  acid  will  produce  this  same  result.  This  acid,  upon 
standing,  changes  to  normal  stannic  acid  which  is  easily  soluble 
in  acids;  hence,  in  making  use  of  this  reaction  in  the  analysis  ot 
amalgam  alloys,  it  is  not  well  to  allow  the  nitric  acid  solution 
oi  the  alloy  to  stand  too  long  before  filtering. 

Alloys.  —  Pewter  usually  contains  Sn,  Pb,  Cu,  and  Sb,  some- 
times Zn.  Rees's  alloy  Sn  20  parts,  gold  i  part,  and  silver  2 
parts.  Tin  is  also  a  constituent  of  solders,  fusible  metals,  Bab- 
bitt's metal,  bell  metal,  and  bronze. 

An  alloy  of  tin  and  mercury  (tin  amalgam)  is  used  for  "  silver- 
ing mirrors." 

Compounds.  —  The  salts  of  tin  are  not  used  in  medicine  but 
are  useful  as  laboratory  reagents. 

The  chloride  (SnCl2)  prepared  as  suggested  under  properties 
oi  the  metal  is  used  in  solution  as  a  test  for  mercury. 


METALS  OF  GROUP  II  41 

The  stannic  salts  are  the  more  stable  and  this  solution  of 
stannous  chloride  easily  becomes  stannic  chloride  unless  excess 
of  metallic  tin  is  kept  in  the  solution. 

Stannous  nitrate  may  be  produced  by  the  action  of  cold 
nitric  acid  as  follows: 

4  Sn  +  10HXO3  =  4  Sn(X03).2  +  3  HoO  +  NH4XO3. 

Tin  may  act  as  an  acid-forming  element  in  such  compounds 
as  sodium  stannite  (Na2SnOo)  produced  by  the  solution  of  stan- 
nous hydrate  in  sodium  hydrate, 

Sn(0H)2  +  2  NaOH  =  NagSnOo  +  2  H.O, 

or  sodium  stannate  produced  when  stannic  oxide  is  fused  with 
sodium  hydrate, 

SnOo  +  2  NaOH  =  NaoSnOg  +  H.O. 

Metallic  zinc  thrown  into  a  tin  solution  udll  precipitate  the 
tin  as  follows:     SnCL  +  Zn  =  ZnClo  +  Sn. 

This  reaction  is  used  in  the  separation  of  tin  from  antimony 
in  the  second  group;  and,  in  order  to  obtain  the  tin  in  soluble  form 
suitable  for  a  final  test,  it  is  necessary  to  add  hydrochloric  acid 
sufficient  first  to  dissolve  all  the  zinc  present;  othenvise  it  (tin) 
may  remain  adhering  to  the  zinc. 

Tin,  like  arsenic  and  antimony,  forms  two  series  of  salts,  the 
stannous  (Sn")  and  the  stannic  (Sn^'^).  x\  little  HCl  treated 
with  excess  of  granulated  tin  till  hydrogen  is  no  longer  given  off 
furnishes  a  solution  of  stannous  chloride  suitable  for  the  follow- 
ing experiments : 

Analytical  Reactions.  —  SnClo  with  HoS  gives  brown  pre- 
cipitate of  SnS,  soluble  in  (NH4)2S,  insoluble  in  (NH4)2C03. 

SnClo  with  HgCL  gives  a  white  or  gray  precipitate,  as  ex- 
plained on  page  29  under  "  Mercury,"  and  is  used  as  a  test  for 
presence  of  mercury.  It  may  also  be  used  as  an  alkaloidal  pre- 
cipitant. 

Strong  solutions  of  SnClo  in  presence  of  metallic  Sn  keep 


42      SALTS  OF   THE  METALS  AND  QUALITATIVE  ANALYSIS 

fairly  well,  but  dilute  solutions  without  an  excess  of  tin  oxidize 
very  rapidly  to  stannic  combinations  and  cease  to  be  of  value 
as  reagents. 

Gold,  Au   (Aurum). 

The  Metal.  —  Atomic  weight  197.2.  It  is  usually  found 
uncombined,  but  mixed  wdth  various  impurities.  It  occurs 
frequently  as  native  alloys;  of  these,  two  might  be  mentioned: 
Calverite,  AuTe2,  contains  40%  gold,  and  Sylvanite,  or  graphic 
tellurium,  (AuAg)Te2,  contains  24-26%  gold. 

Gold  is  extracted  from  its  ores  in  various  ways,  the  simplest  of 
which  is  that  known  as  placer  mining.  This  consists  of  a  process 
of  washing  out  the  particles  of  gold  which  separate  themselves 
•easily  because  of  their  hea\aer  weight  compared  to  that  of  the 
gravel  and  stones  among  which  they  are  found.  Hydraulic 
mining,  the  utilization  of  a  great  force  of  water  to  break  up  the 
auriferous  rock,  has  come  to  the  aid  of  placer  mining  in  getting 
the  largest  masses  ready  for  the  washing  process.  Other  methods 
are  quartz  mining  in  which  mercury  is  used  to  attract  the  gold, 
and  the  chlorination  process. 

Properties.  —  Alelting-point  1064°  C.  Pure  gold  is  a  soft 
metal  of  yellow  color,  unless  in  a  very  fine  state  of  subdivision 
produced  by  the  precipitation  of  the  metal  when  the  color  varies 
from  purple  to  brown  or  nearly  black.  Gold  is  more  malleable 
and  more  ductile  than  either  silver  or  copper.  Gold  is  second 
to  silver  as  a  conductor  of  electricity. 

Gold  is  insoluble  in  simple  acids,  but  may  be  dissolved  in 
nitrohydrochloric  acid  (aqua  regia)  with  formation  of  auric 
chloride.  Gold  also  unites  easily  with  bromine  or  iodine,  form- 
ing AuBrs  or  Aula. 

Gold  possesses  the  property  of  adhesiveness  in  a  peculiar 
and  very  marked  degree.  By  virtue  of  this  the  metal  can  be 
welded  without  heat;  continued  hammering  tends  to  lessen  or 
weaken  this  property. 


METALS  OF  GROUP  II 


43 


Wlien  gold-foil  is  heated  to  redness  (annealed)  it  recovers  the 
cohesive  property  which  has  been  largely  lost  by  hammering. 
The  toughness  and  ductibility  are  also  increased.  It  is  recom- 
mended that  the  heating  be  done  in  an  electric  furnace  or  on 
plates  of  mica  or  platinum,  thus  insuring  uniformity  of  effect 
throughout  the  mass  which  it  is  practically  impossible  to  ob- 
tain by  holding  the  metal  in  the  flame.  See  Dental  Cosmos, 
Vol.  XL\T!I,  page  233. 

Non-cohesive  gold,  or  gold  in  which  the  cohesive  property 
cannot  be  developed  by  heating,  may  be  prepared  by  alloying 
or  treatment  with  carbon.  Corrugated  gold  is  of  this  variety 
and  is  prepared,  according  to  Essig,  by 
carbonization  of  unsized  paper  in  inti- 
mate contact  with  the  metal.  See  Essig, 
Dental  Metallurg^^  page  173,  or  Hodgen 
and  Millbury,  page  209. 

Alloys.  —  Gold  is  alloyed  with  copper 
to  make  it  harder  and  more  durable  for 
use  in  the  manufacture  of  jewelry,  plate, 
and  coin.  It  is  alloyed  with  silver  for 
the  purpose  of  reducing  its  melting- 
point.  Copper  and  zinc,  or  copper, 
silver,  and  zinc  may  be  used  in  this 
way  (See  page  13  2  for  formulae  for  gold 
alloys.) 

The  term  "  carat  "  *  as  applied  to  gold  signifies  i/'24  part  and 
is  used  as  a  measure  of  purity  of  an  alloy,  22  carat  gold  being 
22/24  pure  gold.  Twenty  carat  gold  is  20/24  pure,  etc.  The 
amoimt  of  gold  in  a  given  alloy  may  be  determined  approxi- 
mately by  use  of  a  de\ice  «liown  in  Fig.  5,  much  used  by 
jewelers,  consisting  of  a  series  of  standard  alloys  and  a  piece  of 
stone  upon  which  the  test  is  made.     The  tips  are  standard 

*  The  term  carat  is  also  used  by  jewelers  as  a  unit  of  weight.  The  legal  stand- 
ard for  U.  S.,  since  July  i,  1913,  has  been  200  milligrams. 


44     SALTS  OF   THE  METALS  AND  QUALITATIVE  ANALYSIS 

alloys.  Parallel  markings  are  made  on  the  stone  with  the  alloy 
in  question  and  with  the  tip  supposed  to  correspond  to  it;  then 
the  addition  of  a  drop  of  strong  nitric  acid  to  the  marks  and  a 
careful  comparison  of  their  appearance  will  show  if  the  two  are 
of  the  same  composition. 

If  the  composition  of  an  alloy  is  known,  the  value  in  carats 
may  be  determined  by  the  following: 

Rule  to  determine  the  carat  of  a  given  alloy:  Multiply  24 
by  the  weight  of  gold  used  and  divide  result  by  total  weight  of 
alloy.  For  instance,  if  an  alloy  is  made  containing  9  parts  of 
gold  and  3  of  another  metal,  the  total  weight  will  be  12  and 
the  calculations  24X9^  12  =  18.  The  alloy  is  an  i8-carat 
gold. 

Gold  may  be  raised  to  a  higher  carat  by  the  following  rule: 
Multiply  weight  of  alloy  used  by  difference  between  its  carat 
and  that  of  the  metal  to  be  added.  Then  divide  product  by  the 
difference  between  the  carat  of  the  metal  added  and  that  of  the 
required  alloy.  The  figure  thus  obtained  represents  the  total 
weight  of  required  alloy.  Subtract  from  this  the  weight  of  ma- 
terial taken  and  the  difference  is  weight  of  pure  or  alloyed  gold 
to  be  added.     (From  Hall's  Dental  Chemistry.) 

To  reduce  gold  to  a  required  carat  Essig  takes  the  following 
rule  from  Richardson's  Mechanical  Dentistry:  "  Multiply  the 
weight  of  gold  used  by  24  and  divide  the  product  by  the  required 
carat.  The  quotient  is  the  weight  of  the  mass  when  reduced, 
from  which  subtract  the  weight  of  the  gold  used,  and  the  remain- 
der is  the  weight  of  the  alloy  to  be  added." 

Analytical  Reactions.  —  A  one-half  per  cent,  solution  of  AuCla 
may  be  used  in  the  following  tests: 

H2S  with  AuCls  gives  dark  brown  AU2S3  (auric  sulphide), 
soluble  in  yellow  ammonium  sulphide. 

Gold  is  reduced  to  the  metallic  state  by  many  of  the  other 
metals,  as  Pb,  Cu,  Ag,  Sn,  Al,  Sb,  Fe,  Mg,  Zn,  and  Hg;  also 
by  ferrous  sulphate,  stannous  chloride,  and  oxalic  acid. 


METALS  OF  GROUP  II  45 

Add  a  freshly  prepared  solution  of  ferrous  sulphate  to  a  little 
acid  solution  of  AuCls-      Gold  is  precipitated  as  follows: 
AuClg  H-  3  FeS04  =  Au  +  FezCSO^s  +  FeClg. 

Stannous  chloride  precipitates  from  gold  solution  the  "  purple 
of  Cassius,"  consisting  of  a  mixture  of  gold  and  oxide  of  tin  in 
colloidal  forms. 

Gold  is  only  slowly  precipitated  by  oxalic  acid;  2  AuClg  + 
3  H2C2O4  =  6  HCl  +  6  CO2  +  2  Au,  but,  as  Pt  is  not  precipitated 
at  all  by  this  reagent,  it  is  possible  to  separate  Au  and  Pt  in 
solution  of  the  chlorides,  by  this  means. 

KI  will  give  a  dark-green  precipitate  of  Aul2  provided  the 
KI  is  in  excess ;  if  the  gold  is  in  excess,  the  precipitate  is  apt  to  be 
the  yellow  Aul  (aurous  iodide) .  In  the  presence  of  a  considerable 
excess  of  KI  the  Auls  is  kept  in  solution  as  the  potassioauric 
iodide,  KIAUI3.  The  reduction  of  this  double  salt  by  sodium 
thiosulphate  is  made  the  basis  of  the  method  to  determine  the 
quantity  of  Au  in  a  given  alloy,  as  described  in  the  chapter  on 
Volumetric  Analysis. 

PLATrNUM,    Pt. 

The  Metal.  —  Atomic  weight  195.2.  Platinum,  like  gold, 
is  found  principally  in  the  free  or  metallic  state,  often  associated 
with  the  rarer  metals  such  as  iridium,  rhodium,  osmiimi,  and 
palladium;  also  combined  with  gold,  silver,  and  copper;  a  native 
arsenide,  PtAs2  is  found  in  the  mineral  sperryHte. 

Properties.  —  Melting-point  nearly  2000°  C.  Platinum  solu- 
bilities are  similar  to  gold;  aqua  regia  forms  the  chloride  PtCU, 
or  the  chloroplatinic  acid  H2PtCl6.  Platimmi  is  a  white  metal 
unaffected  by  oxygen,  or  the  fluids  of  the  mouth,  hence  adapted 
for  use  in  permanent  dental  appHances.  When  melted  it  ab- 
sorbs oxygen  in  a  manner  similar  to  silver  and  when  finely 
divided  (platinum  black)  will  absorb  or  occlude  gases  to  a  re- 
markable degree,  one  part  of  platinum  black  under  favorable 


46      SALTS   OF   THE   METALS  AND  QUALITATIVE  ANALYSIS 

conditions  absorbing  in  this  way  over  eight  hundred  times  its 
volume  of  oxygen.  As  this  occlusion  necessarily  means  conden- 
sation of  the  gas  advantage  may  be  taken  of  this  property  to 
bring  about  chemical  union  of  gases  which  will  not  unite  at  ordi- 
nary temperatures,  such  as  hydrogen  and  oxygen,  oxygen  and 
sulphur  dioxide.  Platinum  black  may  be  made  by  strong  ignition 
of  platinum  chloride. 

Alloys.  —  Platinum  alloys  quite  easily  with  other  metals, 
particularly  lead;  and  platinum  utensils  may  be  destroyed  by 
heating  in  contact  with  the  compounds  of  metals  easily  reduced. 
Sulphur  and  phosphorus  also  attack  platinum. 

Platinum  90%  and  iridium  10%  give  an  alloy  harder,  more 
brittle,  and  more  resistant  to  chemical  action  than  pure  platinum. 

Note.  —  Iridium  is  a  rare  metal  of  particular  interest  in  connection  with  the 
platinum  alloy  given  above.  Its  symbol  is  Ir;  atomic  weight  is  193. i;  melting- 
point  is  about  2500°  C.  It  occurs  with  platinum;  also  associated  with  osmium 
with  which  it  forms  a  very  hard  alloy  insoluble  in  aqua  regia. 

An  alloy  of  platinum  and  osmium  is  practically  insoluble  in 
acids,  is  very  hard  and  capable  of  great  expansion.  Of  the  vary- 
ing proportions  of  the  two  metals  which  may  be  used  those  of  one 
to  ten  per  cent,  of  osmium  with  ninety  to  ninety-nine  per  cent,  of 
platinum  prove  the  most  successful.  One  part  of  osmium  in 
such  an  alloy  will  take  the  place  of  two  and  one  half  times  its 
weight  of  irridium.* 

"  Platinum  color,"  for  coloring  enamel,  is  made,  according 
to  Mitchell's  Dental  Chemistry,  by  precipitating  platinum  from 
a  solution  of  PtCLj  by  boiling  with  KOH  and  grape  sugar;  then, 
grinding  this  finely  divided  platinum  with  feldspar  in  the  pro- 
portion of  one  part  platinum  to  sixteen  parts  feldspar. 

Analytical  Reactions.  —  PtCl4  +  H2S  gives  a  precipitate  of 
sulphide  of  platinum  almost  black,  soluble  in  yellow  ammonium 
sulphide. 

Platinum  solution  with  NH4CI  precipitates  yellow  ammonium 
*  Hepburn,  page  112. 


METALS  OF   GROUP  II 


47 


platinic  chloride,  (NH4)2PtCl6,  crystalline.  Potassium  chloride 
also  gives  a  yellow  crystalline  precipitate  of  KoPtCle,  isomorphous 
with  the  ammonium  compound.  (Plate  III,  Figs,  i  and  3.) 
These  reactions  may  be  made  quantitative  by  using  neutral, 
fairly  concentrated  solutions  and  adding  an  equal  volume  of 
alcohol. 

Both  of  these  double  salts  are  soluble  in  excess  of  alkaH, 
and  reprecipitated  by  HCl. 

Stannous  chloride  reduces  PtCU  to  PtCL:  but  forms  no  pre- 
cipitate. jNIetaUic  Zn  wall  precipitate  platinum  as  a  fine  black 
powder  or  spongy  mass. 


Analysis  of  Group  II. 

Separation  of  parts  (a)  and  ih) 

A  portion  of  the  clear  filtrate,  from  Group  I,  containing  a 
shght  excess  of  HCl  is  tested  for  metals  of  Group  II  by  the 
addition  of  HoS  water.* 

If  a  precipitate  is  obtained,  warm  the  -tC'/zo/g  of  the  solution 
and  pass  in  HoS  gas  for  from  three  to  five  minutes,  which  pre- 
cipitates all  metals  of  the  group  as  sulphides.     Filter. 

Break  point  of  filter-paper  with  glass  rod  and  wash  Group  II 
into  beaker  with  warm  (NH4)2S;    digest  hot  for  a  few  minutes. 

Filter  and  wash  the  precipitate  till  wash-water  shows  only 
traces  of  CI.     Throw  away  all  wash-water  except  the  first. 


Group  II  (d).     Cu,  Cd,  Bi,  Hg,  and  Pb. 


Group  H  {b).     As,  Sb,  Sn,  Au,  and  Pt. 


*  A  preliniinar>'  test  is  made  on  a  part  of  the  solution  because  in  the  absence 
of  Group  n,  the  analysis  of  Group  III  can  be  made  more  easily  ^-ithout  the  pres- 
ence of  H2S. 


48      SALTS  OF   THE   METALS   AND  QUALITATIVE  ANALYSIS 

Analysis  of  Group  II  (a). 
Dissolve  the  precipitate  off  the  paper  with  hot  dilute  HXO3. 


Hg,  if  present,  will  remain  on  paper,  black. 
Filtrate  contains  nitrates  of  Pb,  Cu,  Cd,  and  Bi. 


Test  black  residue  on  paper  for  Hg"  by  dissolving  in  aqua 
regia  and  precipitating  with  SnCl2.  For  reaction  between  SnCl2 
and  HgClo,  see  page  29.  Aqua  regia  may  be  made  by  mixing 
two  or  three  parts  of  HCl  with  one  part  of  HNO3.  Free  CI  is 
liberated  which  dissolves  the  HgS  as  HgCb. 

3  HCl  +  HNO3  =  NOCl  +  2  HoO  +  CI2. 

If  lead  is  present  in  Group  I,  the  filtrate  above  will  contain 
traces  which  must  be  separated  by  adding  a  few  drops  of  H2SO4 
and  allowing  to  stand  at  least  fifteen  minutes.     Filter. 


PbSOj  remains  on  paper. 
Filtrate  contains  Cu,  Cd,  Bi. 


To  the  filtrate  add  NH4OH  till  alkaline;  Bi  separates  as  Bi 
(0H)3,  white.  Filter.  Confirmatory  test  for  bismuth  may  be 
made  by  pouring  over  the  precipitated  Bi(0H)3  on  the  paper  a 
solution  of  sodium  stannite.  If  bismuth  is  present  the  precipitate 
turns  black  in  accordance  with  the  reaction  given  on  page  31. 


METALS   OF   GROUP  II 


49 


Bi(0H)3 


Cu  and  Cd. 


Dmde  the  filtrate  (Cu  and  Cd)  into  two  parts.  A  blue  color 
indicates  presence  of  Cu.  With  one  part  test  for  Cu  by  making 
it  acid  with  acetic  acid  and  adding  K4FeCy6,  which  will  give 
a  brown  precipitate  of  CuoFeCye-  With  the  other  part  test  for 
Cd  by  adding  solid  KCN  very  carefully  till  all  blue  color  has 
disappeared;  then  a  Httle  H2S  w^ater  will  give  a  yellow  preci- 
pitate of  CdS  if  cadmium  is  present. 

Analysis  of  Group  II  (b). 

To  the  ammonium  sulphide  solution  add  HCl  till  acid.  A 
very  fine  white  precipitate  may  be  sulphur  only. 

Filter  and  wash.  Throw  away  wash-water.  Pierce  paper 
and  wash  sulphides  into  large  test-tube  or  small  beaker.  Add 
10  c.c.  of  (NH4)2C03  and  heat  for  a  few  minutes.    Filter. 


Sb,  Sn,  Au,  Pt  sulphides  are  on  the  paper. 


Arsenic  sulphide  is  in  the  filtrate. 


Add  HCl  and  Zn  and  make  Gutzeit's  test  (page  34)  and  if 
necessary  Fleitmann's  (page  36)  or  Marsh's  (page  35). 

Dry  this  precipitate  upon  paper  and  place  paper  and  pre- 
cipitate in  a  porcelain  evaporator,  add  concentrated  HCl  and 
heat.  (This  77iust  be  done  under  the  hood.)  Dilute  and  filter, 
when  Au  and  Pt  will  remain  undissolved. 


50      SALTS  OF   THE  METALS  AND  QUALITATIVE  ANALYSIS 


Au  and  Pt. 


Sb  and  Sn. 


To  the  Sb  and  Sn  solution  add  a  little  Zn  and  a  piece  of 
platinum-foil.  The  antimony  and  tin  will  both  be  reduced  to 
the  metallic  state,  the  Sb  being  deposited  on  the  Pt  as  a  brown 
or  black  coating.  Presence  of  Sb  may  be  confirmed  by  remov- 
ing the  Pt,  washing  carefully,  treating  with  (NH4)2S,  and  dry- 
ing, when  the  coating  will  become  Sb2S3,  orange-red. 

To  the  solution  to  be  tested  for  Sn  add  HCl  enough  to  dis- 
solve all  the  Zn  which  has  been  added,  filter,  and  test  filtrate 
with  HgCl2  (page  29). 

Dissolve  the  insoluble  residue  of  Au  and  Pt  (the  residue 
will  be  dark-colored  if  either  of  these  metals  are  present)  in 
aqua  regia  and  divide  solution  into  two  parts. 

Test  one  part  for  gold  with  solution  of  FeS04,  or  a  mixture 
of  SnCl2  and  SnCU  (page  45). 

Test  the  other  part  for  Pt  by  adding  NH4CI,  allow  to  stand 
over  night  adding  a  little  alcohol,  and  a  precipitate  of  ammo- 
nium platinic  chloride  will  be  obtained,  yellow  and  crystalline 
(see  Plate  III,  Fig.  i,  page  171). 


METALS   OF  GROUP  II 


SI 


OUTLINE   SCHEME   FOR  ANALYSIS  OF   GROUP   II. 


To  the  warmed  filtrate  from  Group  I  add  H2S. 
As,  Sb,  Sn,  Au,  Pt,  Cu,  Cd,  Bi,  Hg,  and  Pb. 
Filter  and  treat  with  warm  (NH4)2S. 


A  ppt.  may  be  sulphides  of 


Residue  is  Group  II  {a),  page  47,  and  consists 

of  sulphides  oj  Cu,  Cd,  Bi.  Hg,  and  Pb. 
Treat  on  paper  c  warm  dil.  HNO3. 


Residue 

isHg. 

Dissolve 

in  aqua 

regia  and 

test  c 

SnClj 

(page  29) . 


Solution   Cu,    Cd,   Bi,  and  Pb. 
Add  H2SO4  and  filter. 


Ppt. 

is 

PbS04 


Solution  is  Cu,  Cd,  and 
Bi.   AddNH40Hand 

filter. 


Ppt.  is 
Bi(0H)3 


Solution  is  Cu  and 
Cd. 


Test  for 
Cu5HA 

and 
KiFeCye.i 

(page  49.) 


Test  for 
Cd5KCN 
and  H2S. 


Solution= As,  Sb,  Sn,  Au,  and  Pt.  Reprecipitate 
c  HCl,  filter  and  treat  ppt.  c  strong  (NHjjjCOj 
sol. 


Residue  =  Sh,  Sn^Au,  and  Pt,  sul- 
phides. Treat  c  cone.  HCl,  dilute 
and  filter. 


Residue. 
Au  and  Pt.     Dissolve 
in  aqua  regia  and  di- 
vide. 


Part  I. 

Test  for 

Au  c  FeS04 

(page  45). 


Part  II. 
Test  for 

Pt3 
NH4CI 
and  alco- 
hol. 


Solution. 

Sb  and  Sn. 
Test  for 
SbcPt 

foil  and  Zn. 


Test  for 
Sn  in  fil- 
trate c 
HgCh 
(page  50). 


Solution. 

As.    Make 
Gutzeit's 
or  Fleit- 
mann's 

test  for  As 
(pages  34 
and  36) . 


QUESTIONS  ON  GROUP  11. 

Why  is  it  necessary  to  wash  the  precipitate  of  Group  II 
practically  free  from  CI  before  dissolving  in  warm  HNO3  ? 

How  does  the  Hg  found  in  Group  II  differ  from  the  Hg  in 
Group  I  ? 

Does  the  Pb  found  in  Group  II  differ  from  the  Pb  in 
Group  I  ? 

Before  making  the  final  test  for  Sn,  why  is  it  necessary  to 
dissolve  all  the  Zn  which  has  been  added  ? 

In  precipitating  Group  II  why  should  the  solution  be  made 
acid  with  HCl  before  adding  HoS? 

\^^ly  is  it  better  to  use  HoS  gas  rather  than  HoS  water  in 
precipitating  metals  of  Group  II  ? 

Before  testing  for  Cd  why  add  KCN  to  decolorize  the  copper 
solution  ? 


52      SALTS  OF  THE  METALS  AND  QUALITATIVE  ANALYSIS 

Why  is  a  confirmatory  test  for  bismuth  desirable  ? 

Why  must  organic  matter  be  destroyed  before  making  Marsh's 
test  for  arsenic  ? 

What  reagent  would  you  select  for  the  precipitation  of  gold 
and  give  reason  for  choice  ? 

Why  is  sulphuric  acid  preferable  to  hydrochloric  in  making 
Marsh's  test  for  arsenic  ? 


CHAPTER   V. 
METALS   OF   GROUP  m. 

Iron,  Fe  (Ferrum). 

The  Metal.  —  Atomic  weight  55.84.  Iron  occurs  widel}; 
distributed  in  nature  combined  with  oxygen  as  Magnetite  01 
magnetic  iron  ore,  Fe304;  as  Red  Hematite,  Fe-iOs;  or  Brown 
Hematite  or  Limonite,  2  Fe203.3  H2O;  with  sulphur  as  Iron 
Pyrites  or  Fool's  Gold,  FeSs;  and  with  carbon  as  Spathic  iron 
ore  or  Siderite,  FeCOs. 

The  reduction  of  iron  from  its  ores  is  typical  of  one  of  the  four 
general  methods,  that  is,  reduction  by  carbon.  This  is  carried 
out  in  the  blast  or  smelting  furnaces,  which  are  so  constructed 
that  a  supply  of  coal,  iron  ore,  and  suitable  flux  may  be  intro- 
duced at  the  top  of  the  furnace.  The  fusible  slag  consisting  of 
the  flux  which  has  dissolved  the  impurities  of  the  ore  and  the 
purified  molten  metal  is  drawn  off  from  the  bottom,  thus  admit- 
ting a  continuous  process.  This  melted  iron,  cast  in  molds  as 
it  comes  from  the  furnace,  constitutes  our  cast  or  pig  iron,  is 
brittle,  and  contains  a  considerable  proportion  of  carbon,  some- 
times as  much  as  two  and  three- tenths  per  cent.,  and  other  im- 
purities. 

Wrought  iron  is  produced  by  working  melted  iron  in  specially 
constructed  furnaces  so  that  the  greater  part  of  the  impurities 
are  removed.  It  contains  less  than  six-tenths  of  a  per  cent,  of 
carbon. 

Steel  may  be  made  by  a  more  perfect  removal  of  impurities 
in  the  Bessemer  converter  and  subsequent  mixture  of  exact  pro- 
portions of  carbon,  phosphorus,  and  manganese.  Steel  contains 
from  six-tenths  to  one  and  six-tenths  per  cent,  of  carbon. 

53 


54     SALTS  OF   THE  METALS  AND  QUALITATIVE  ANALYSIS 

Reduced  iron  or  "  iron  by  hydrogen  "  is  prepared  by  the 
reduction  of  the  heated  oxide  or  hydroxide  in  a  stream  of  hydro- 
gen gas,  and  consists  of  a  very  fine  powder  of  pure  metalhc  iron. 

Properties.  —  Melting-point  1275°  C.  Iron  dissolves  in 
hydrochloric  or  sulphuric  acid  with  the  evolution  of  hydrogen. 
In  nitric  acid,  cold  and  dilute,  ferrous  and  ammonium  nitrates 
are  produced.  Warm  dilute  nitric  acid  forms  ferric  nitrate  and 
nitric  oxide.  Iron  is  most  magnetic  of  all  metals;  next  in  this 
particular  come  nickel  and  cobalt. 

Compounds.  —  Iron  forms  two  classes  of  salts,  ferrous, 
represented  by  ferrous  sulphate,  FeS04;  and  ferric,  represented 
by  ferric  sulphate,  Fe2  (804)3,  or  ferric  chloride,  FeCla. 

Ferric  sulphate,  also  known  as  Monsel's  salt,  is  used  as  a 
styptic. 

Ferric  chloride,  FeCls  or  FcoCIg,  is  made  by  dissolving  iron 
in  hydrochloric  acid,  oxidizing  the  ferrous  chloride  with  nitric 
acid,  and  then  driving  off  the  nitric  acid  by  evaporation.  The 
resulting  solution,  however,  contains  traces  of  free  nitric  and 
considerable  free  hydrochloric  acid.  In  the  tincture  of  chloride 
of  iron  these  acids  react  with  the  alcohol  forming  various  ethers, 
to  which  the  peculiarities. of  the  tincture  may  be  due. 

Copperas  and  green  vitriol  are  commercial  names  for  crys- 
tallized ferrous  sulphate,  FeS04.7  H2O,  which  is  used  as  a  disin- 
fectant and,  to  a  slight  extent,  in  medicine  as  an  astringent. 

Ferrous  carbonate,  (FeC03)it;(Fe(OH)2)y,  prepared  by  double 
decomposition  between  ferrous  sulphate  and  potassium  or  so- 
dium carbonate,  is  a  medicinal  preparation  quite  largely  used 
as"  Blaud's pills." 

Analytical  Reactions.  —  A  solution  for  demonstrating  the 
reactions  of  ferrous  salts  is  best  made  by  saturating  cold  dilute 
sulphuric  acid  with  clean  iron  wire.  A  three  to  five  per  cent,  solu- 
tion of  fresh  crystals  of  ferrous  ammonium  sulphate  may  be  used. 
The  ordinary  ferrous  sulphate  or  "  copperas  "  is  almost  sure  to 
contain  some  ferric  salt.     Use  a  two  to  three  per  cent,  solution  of 


METALS  OF  GROUP  III  55 

ferric  chloride  and  make  the  following  tests,  comparing  the  de- 
portment of  the  ferrous  and  ferric  solutions  with  each  reagent. 
Write  the  reactions. 

H2S  with  pure  ferrous  salts  gives  no  reaction;  with  ferric 
salts  the  iron  is  reduced  to  the  ferrous  combination,  but  gives  no 
precipitate  except  sulphur. 

(NH4)2S  gives  with  ferrous  iron  a  black  precipitate  of  FeS; 
with  ferric  salts  it  gives  a  precipitate  containing  FeS  and  S. 

NH4OH  precipitates  Fe"  as  ferrous  hydroxide,  Fe(0H)2; 
white  if  perfectly  pure,  but  usually  a  dirty  green  from  admixture 
of  ferric  compounds.  The  presence  of  NH4CI  prevents  a  complete 
precipitation  as  Fe(0H)2. 

With  ferric  salts,  NH4OH  completely  precipitates  the  iron 
as  brick-red  ferric  hydroxide,  Fe(0H)3. 

K4FeCy6  gives  with  ferrous  salts  a  bluish-white  precipitate 
of  potassium  ferrous  ferrocyanide,  K2FeFeCy6. 

With  a  solution  of  ferric  salts  the  deep  Prussian  blue,  ferric 
ferrocyanide,  Fe4(FeCy6)3,  is  thrown  out. 

With  potassium  ferricyanide,  ferrous  salts  give  a  dark-blue 
precipitate  of  ferrous  ferricyanide,  Fe3(FeCy6)2-  With  ferric 
salts  no  precipitation  occurs,  but  the  color  may  change  to  green 
or  brown. 

KCyS  or  NH4CyS  gives  no  reaction  with  pure  ferrous  salts, 
but  with  ferric  salts  a  deep  red  solution  of  ferric  thiocyanate, 
Fe(CyS)3,  is  produced.  This  red  color  is  destroyed  by  addition 
of  HgCl2,  not  affected  by  HCl,  and  may  be  extracted  from  the 
aqueous  solution  by  shaking  with  ether  in  which  the  Fe(CyS)3  is 
soluble. 

Aluminium,  A1. 

The  Metal.  —  Atomic  weight  27.1.  Aluminium  as  a  con- 
stituent of  clay,  feldspar,  mica,  etc.,  constitutes  a  considerable 
part  of  the  earth's  crust.  The  principal  sources  are  Cryolite, 
Bauxite,  and  Corundum. 


56      SALTS  OF   THE  METALS  AND  QUALITATIVE  ANALYSIS 

Properties.  —  Melting-point  657°  C.  Aluminium  is  a  silver 
white  metal,  a  good  conductor  of  heat  and  electricity,  and  one 
of  the  Hghtest  metals,  its  specific  gravity  being  2.58.  Aluminium 
is  reduced  in  an  electric  furnace  by  the  aid  of  charcoal  and  copper 
with  which  it  amalgamates  (Cowle's  process). 

Alloys.  —  Aluminium  alloys  are  not  difficult  to  produce. 
The  pure  metal  is  used  in  making  plates.  A  high  proportion  of 
aluminium  in  alloys  is  not  desirable  as  it  renders  the  alloy  ex- 
tremely brittle.  Alloys  containing  from  live  to  thirty  per  cent. 
are  of  increasing  importance.  Aluminium  bronze  consisting  of 
copper  with  five  to  twelve  per  cent,  of  aluminium  is  used  as  a 
base  for  artificial  dentures.  An  alloy  used  in  the  preparation  of 
analytical  balances  and  scientific  apparatus  known  as  MagnaUum 
contains  aluminium  and  magnesium. 

Compounds.  —  The  most  important  soluble  salts  of  alu- 
minium are  ammonia  alum,  NH4A1(S04)2  12  HoO,  potash  alum, 
KA.1(S04)2  12  H2O,  and  aluminium  sulphate,  Al2(S04)3. 

The  term  alum  is  applied  to  any  salt  of  definite  crystalline 
form  containing  one  molecule  of  a  univalent  sulphate,  such  as 
K2SO4  or  Na2S04,  combined  with  one  molecule  of  a  trivalent 
sulphate,  AI2  (804)3,  Fe2 (804)3  or  Cr2  (804)3,  and  crystalUzed  with 
twenty-four  molecules  of  water.  The  formula  of  alum,  as  given 
above,  comprises  just  one-half  of  this  combination.  Alum  need 
not  contain  any  aluminium  whatever  so  long  as  it  conforms  to  the 
foregoing  requirements,  e.g.,  chrome  alum  may  be  NH4Cr (804)2 
12  H2O  and  ferric  alum  is  usually  NH4Fe(S04)2 12  H2O. 

Analytical  Reactions.  —  Use  a  5%  solution  of  either  of  these 
for  the  following  tests: 

AI2  (804)3  with  (NH4)28  and  H2O  gives  a  white  precipitate  of 
A1(0H)3.     Write  the  reaction. 

A1(0H)3  is  Hkewise  produced  by  NH4OH,  Na2C03,  or  NaOH; 
the  precipitate  is  soluble  in  excess  of  fixed  alkali  hydroxides  with 
formation  of  aluminates: 

A1(0H)3  +  KOH  =  KAIO2  +  2  H2O. 


METALS  OF  GROUP  III  57 

The  alkaline  peroxides  produce  aluminates  from  A1(0H)3. 
Demonstrate  by  covering  a  little  precipitated  aluminium  hy- 
droxide in  a  porcelain  dish  with  a  very  little  water;  then  sprinkle 
on  to  the  mLxture  sodium  peroxide  in  small  portions  till  a  clear 
solution  results.  Nitric  or  hydrochloric  acid  will  decompose  the 
aluminate  forming  again  the  aluminium  salt,  which  can  be 
reprecipitated  by  ammonia  as  A1(0H)3. 

The  alkaHne  aluminates  may  also  be  formed  by  fusion  with 
Na2C03  and  KNO3  and  then  may  be  dissolved  in  hot  water. 

From  the  solution  of  KAIO2  the  Al  may  be  precipitated  as 
A1(0H)3  by  excess  of  NH4CI  (difference  from  Zn,  page  66). 

The  presence  of  organic  acids,  tartaric,  oxaHc,  etc.,  inter- 
feres with  the  precipitation  of  aluminium  hydroxide  and  may 
entirely  prevent  it.  The  presence  of  ammonium  chloride  favors 
its  precipitation. 

"Chromium,  Cr. 

The  Metal.  —  Atomic  weight  52.  Occurs  as  chrome  iron  ore 
or  chromite,  FeOCr203. 

Properties.  —  Chromium  is  a  hard,  grayish  colored  metal, 
not  used  as  such  in  dentistry. 

Compounds.  —  Chromium  forms  two  oxides,  one  basic  in 
character,  Cr203,  which  forms  the  basis  of  chromic  salts,  as  Cvi 
(504)3,  Cr2Cl6(CrCl3),*  etc. ;  the  other,  Cr03,  is  an  acid  anhydride, 
crystallizes  as  dark-red  needles,  and  gives  rise  to  two  series  of 
salts:  neutral  chromates,  such  as  K2Cr04,  and  acid  chromates 
or  dichromates,  K2Cr207. 

Analytical  Reactions.  —  The  soluble  chromic  salts  most 
easily  obtained  are  chrome  alum,  KCr(S04)2,  chromic  sulphate, 
Cr2(S04)3,  and  chromic  chlorid-e,  CrCls.  With  a  5%  solution  of 
either  of  these  the  following  may  be  demonstrated : 

Cr2 (804)3  with  (NH4)2S  gives  greenish  precipitate  of  Cr(0H)3. 

*  There  is  a  series  of  chromous  salts,  CrCl2,  Cr(0H)2,  etc.,  corresponding  to 
a  chromous  oxide,  CrO,  but  the  oxide  itself  is  not  known. 


58      SALTS   OF   THE   METALS  AND  QUALITATIVE  ANALYSIS 

Similarly  to  aluminium,  the  chromium  hydroxide  is  precipi- 
tated by  the  alkahne  carbonates  and  the  alkaline  sulphides  as 
well  as  by  the  hydroxides;  and  then  by  boihng  the  Cr(0H)3  with 
NaOH  or  KOH,  or  by  fusing  with  NaaCOg  and  KNO3,  or  by  the 
action  of  sodium  peroxide  and  heat,  chromates  of  the  alkalis 
may  be  produced.  The  chromate  upon  the  addition  of  nitric 
acid  becomes  the  dichromate.  This  solution  after  neutraHzation 
with  ammonia  will  give  a  characteristic  yellow  precipitate  of 
PbCr04  with  soluble  salts  of  lead. 

The  soHd  dichromate  K2Cr207  with  strong  H2SO4  gives,  in 
the  presence  of  chlorides,  the  reddish-brown  gas  Cr02Cl2  (chloro- 
chromic  anhydride  or  chromium  dioxychloride)  used  as  a  test  for 
chlorides  (page  96) . 

Analysis  of  Group  III. 

(Fe,  Al,  Cr.     Phosphates  and  oxalates  being  absent.) 

The  filtrate  from  Group  II  must  be  freed  from  H2S  by  boil- 
ing with  a  few  drops  of  HNO3  in  a  porcelain  dish  till  a  drop  re- 
moved by  a  glass  rod  does  not  blacken  filter-paper  wet  with  a 
solution  of  lead  acetate.  This  treatment  also  serves  to  oxidize 
the  iron  (reduced  by  H2S)  to  ferric  salt  and  at  the  same  time 
concentrates  the  solution.  To  the  clear  solution  thus  obtained 
add  10  c.c.  of  NH4CI  solution,  then  NH4OH  till  alkahne,  when 
the  metals  of  this  group  will  separate  as  hydroxides:  Fe(0H)3 
brick-red,  A1(0H)3  white,  Cr(0H)3  bluish-green.  Filter  and 
wash. 


Group  Til. 

Groups  IV,  V,  and  VI. 


METALS  OF  GROUP  III  59 

Transfer  the  precipitated  hydroxides  to  a  porcelain  dish. 
Cover  with  a  little  water.  Add  in  small  portions  sodium  per- 
oxide not  exceeding  in  total  bulk  the  original  precipitate.  Add 
a  little  more  water  and  boil  till  oxygen  ceases  to  be  evolved,  add- 
ing water  if  necessary  to  keep  up  the  volume  of  the  solution. 
Filter  out  iron  if  it  is  present. 


Fe(0H)3. 

Al  and  Cr  as  negative  ions. 


Wash  the  precipitate  remaining  on  the  paper  (Fe)  and  dis- 
solve in  dilute  HCl.  Divide  resulting  solution  (FeCls)  into  two 
parts  and  confirm  presence  of  Fe  by  testing  one  with  K4FeCy6 
(blue  precipitate)  and  the  other  with  KCyS  (red  solution). 

If  iron  is  found,  determine  in  original  substance  whether 
ferrous  or  ferric,  by  use  of  tests  described  on  page  55. 

To  the  filtrate  containing  sodium  aluminate  and  chromate 
add  HNO3  producing  A1(N03)3  and  Cr207=.  Add  5  c.c.  of  ten 
per  cent.  NH4CI  solution  and  make  alkaline  with  NH4OH,  which 
precipitates  Ai(0H)3.  Filter,  acidify  filtrate  with  acetic  acid 
and  test  for  presence  of  chromium  with  lead  acetate  solution. 
(Precipitate  is  PbCr04.) 

The  presence  of  aluminium  may  be  confirmed  as  follows: 

Transfer  the  precipitate  of  aluminium  hydroxide  to  a  small 
evaporating  dish,  moisten  with  concentrated  nitric  acid,  add  a 
very  tiny  crystal  of  cobalt  nitrate,  and  evaporate  to  dryness. 
Let  the  blue  flame  (O.F.)  of  ^he  Bunsen  burner  play  directly 
upon  the  residue  in  the  dish.  Aluminium  produces  the  blue 
cobalt  aluminate. 

The  aluminium  hydroxide  should  be  as  nearly  white  as  pos- 
sible.    If  it  is  dark  in  color,  dissolve  it  in  nitric  acid  and  repre- 


6o      SALTS  OF   THE  METALS  AND  QUALITATIVE  ANALY^SIS 

cipitate  with  ammonium  hydroxide  before  treating  with  cobalt 
nitrate.* 


OUTLINE  FOR  ANALYSIS  OF  GROUP  III. 

Take  clear  filtrate  from  Group  II  and  boil  with  a  few  drops  of  HNO3  to  expel 
H2S  and  oxidize  Fe".     Add  NH4CI  and  NH4OH  and  filter. 


Ppt.    A1(0H)3 .  Cr(0H)3 .  Fe(0H)3.    Treat    with    Na202.    Boil    5    H2O. 
Filter  (page  58). 


Ppt.  Pe(0H)3.  Test 
5KCNSandK4Fe 
(CN)6  (page  59)- 


Sol.  NaAlO,  and  Na2Cr04.    Add  HN03=A1-H-+  and 
(Cr207)=.    Add     NH40H=A1(0H)3    and    Cr04=. 

Filter. 


Test  for  Al  5  Co(N03)2 

(page  59). 


Test  for  Cr04    c 

Pb(C2H302)2 


Solution. 
Groups    IV,  V, 
and  VI 


QUESTIONS  ON  GROUP  III. 

Why  boil  off  H2S  before  precipitating  the  group  with  NH4OH? 
Why  add  HNO3? 

In  making  final  test  for  chromium  why  is  it  necessary  to 
acidify  with  acetic  acid? 

What  is  the  action  of  the  peroxide  of  sodium  in  the  separation 
of  aluminium  and  chromium? 

Why  is  it  necessary  to  test  the  original  solution  to  determine 
the  character  of  the  iron? 

*  For  the  detail  of  this  test  as  well  as  for  the  general  method  of  separation 
of  this  group  by  use  of  sodium  peroxide,  the  author  is  indebted  to  Miss  Mary  E. 
Holmes,  Associate  professor  of  Chemistry  at  Mount  Holyoke  College. 


CHAPTER  VI. 
METALS    OF   GROUP   IV. 

Cobalt,  Co. 

The  Metal.  —  Atomic  weight  58.97.  Cobalt  occurs  in  nature 
as  an  arsenide  C0AS2,  smaltite;  also  CoAsS,  cobaltite.  These 
ores  are  poisonous  and  have  in  times  past  caused  the  miners  so 
much  trouble  that  the  name  cobalt  was  apphed  to  them,  the 
word  meaning,  "  A  demon  or  mountain  sprite."  Metallic  arsenic 
has  also  been  called  cobalt.  These  facts  are  probably  responsible 
for  an  undeserved  reputation  which  is  sometimes  attached  to 
the  pure  oxide  of  cobalt. 

Analjrtical  Reactions.  —  Use  a  2%  solution  of  nitrate.  Crys- 
talline salts  of  cobalt  are  usually  of  pink  color;  anhydrous 
salts  are  blue. 

Co(N03)2  with  (NH4)2S  gives  precipitate  of  cobalt  sulphide, 
black.     Test  solubihty  of  this  precipitate  in  HCl. 

Make  a  borax  bead  by  fusing  a  little  borax  on  the  looped  end  of 
a  clean  platinum  wire.  When  a  bead  of  clear  ''  borax  glass  " 
has  been  obtained,  dip  it  in  a  little  of  the  cobalt  sulphide  just 
formed,  and  fuse  again.  The  color  of  the  bead  when  cold  is  a 
deep  blue. 

Note.  —  Be  sure  and  make  the  fusion  complete;  the  use  of  an  insufficient 
amount  of  heat  will  account  for  much  of  the  trouble  experienced  by  students  in 
obtaining  satisfactory  bead  tests. 

Co(N03)2  with  KNOo  forms  a  double  nitrite,  Co(N02)2 
2  KNOo,  soluble  in  water;  but  if  sufficient  acetic  acid  is  added 
to  produce  a  strong  acid  reaction,  the  solution  heated,  and  then 
allowed  to  stand  overnight,  the  cobalt  is  completely  precipitated 
as  another  double  salt,  Co(N02)2,  3  EINO2,  yellow  and  crystalline. 

61 


62      SALTS  OF   THE  METALS  AND  QUALITATIVE  ANALYSIS 

Nickel,  Ni. 

The  Metal.  —  Atomic  weight  58.68.  It  occurs  associated 
with  Cobalt,  sometimes  with  Iron  or  with  Copper  as  a  sulphide. 
Also  it  is  found  combined  with  magnesium  as  a  double  silicate 
called  Garnierite,  NiMg(Si03)2.3  H2O.  Natural  alloys  of  nickel 
with  arsenic  and  with  antimony  are  to  be  included  among  the 
sources  of  the  metal. 

Properties.  —  The  metal  is  white  and  hard,  and  has  a  high 
melting-point.  It  is  soluble  in  dilute  mineral  acids,  most  easily 
in  nitric.  It  is  the  least  malleable  of  the  common  metals.  It 
tarnishes  very  slowly  in  the  air. 

Alloys.  —  The  principal  alloys  are  German  silver,  containing 
copper,  nickel,  and  zinc,  and  an  alloy  of  25%  nickel  and  75%  cop- 
per used  by  the  United  States  Government  in  making  five  cent 
pieces. 

In  contact  with  saliva  German  silver  changes  rapidly,  and 
in  consequence  is  usually  gold  plated  when  used  for  orthodontia 
appliances. 

Nickel  plating.  —  Nickel  is  largely  used  for  plating  steel 
and  copper.  In  this  process  metallic  nickel  is  made  the  positive 
pole  and  substances  to  be  plated  are  attached  to  the  negative 
pole  of  a  battery  giving  not  more  than  five  volts.  The  electro- 
lyte is  a  solution  of  nickel  and  ammonium  sulphate  made 
slightly  alkaline  with  ammonia  water.  Nickel  deposits  on 
copper  in  a  much  more  satisfactory  manner  than  on  iron,  and 
from  warm  solution  better  than  from  cold. 

The  following  formulae  are  also  recommended  by  Prinz:* 

Nickel  sulphate 10  parts 

Sodium  citrate .' 9 

Distilled  water 280     " 

Nickel  and  ammonium  sulphate 70  parts 

Boric  acid 25 

Distilled  water 1000     " 

In  any  case  use  pure  nickel  in  sheet  form  as  an  anode. 

*  Dental  Formulary. 


METALS  OF  CROUP  IV  63 

Analytical  Reactions.  —  Use  a  2%  solution  of  the  sulphate 
or  nitrate.  XiSO^  with  (NH4)2S  gives  XiS,  black.  Test  solu- 
bility in  HCl. 

The  borax-bead  test  appUed  to  NiS  or  other  nickel  salt  gives 
a  bead  yellowish  brown  when  cold,  but  the  color  is  easily  masked 
by  other  metals. 

Ni  salts  with  KNO2  give  the  soluble  double  nitrite  of  sim- 
ilar composition  to  the  Co  salt,  Xi(N02)2,  2  KXOo.  The  nickel 
salt,  unlike  the  cobalt,  is  not  easily  decomposed,  and  is  not 
precipitated  by  heating  ^"ith  acetic  acid.  Advantage  is  taken 
of  this  fact  in  effecting  the  separation  of  cobalt  from  nickel 
(page  61). 

Manganese,  ]SIn. 

The  Metal.  —  Atomic  weight  54-93.  Occurs  chiefly  as  the 
dioxide  ^MnOi,  p}ToIusite. 

Compounds.  —  The  black  oxide,  manganese  dioxide,  is 
commercially  important  in  the  production  of  chlorine.  By 
Weldon's  process,  the  chlorine  is  obtained  from  hydrochloric 
acid,  the  p}Tolusite  acting  as  an  oxidizing  agent. 

The  oxidation  of  manganese  dioxide  in  the  presence  of  potas- 
sium hydroxide  results  in  the  formation  of  potassium  permanga- 
nate, K^In04.  This  salt  is  a  valuable  disinfectant  and  is  largely 
used.  Its  decomposition  furnishes  five  atoms  of  available  ox}'gen 
from  ever}'  double  molecule  (Ko^NInaOg). 

Condy's  fluid,  a  commercial  disinfectant,  is  a  solution  of 
potassium  permanganate. 

Manganese  salts  are  usually  flesh-colored. 

Analjrtical  Reactions.  —  A  three  per  cent,  solution  of  the  sul- 
phate may  be  used  in  the  f ollowdng  tests : 

MnSO^  with  (XTIilaS  gives  flesh-colored  precipitate  of  MnS. 
Test  solubility  in  HCl.  With  a  Httle  of  the  precipitated  ^InS 
make  a  red-lead  test  for  Mn  as  follows: 

Place  in  a  test-tube  a  Httle  red  lead  (Pb304).     Add  three  or 


64      SALTS  OF   THE  METALS  AND  QUALITATIVE  ANALYSIS 

four  cubic  centimeters  of  a  solution  of  nitric  acid  (about  one  part 
of  concentrated  HNO3  and  one  of  H2O),  and  boil  well.  Add, 
by  means  of  a  glass  rod,  a  little  of  the  washed  MnS  to  the  mixture 
in  the  tube  and  boil  again.  Now  dilute  with  water  till  the 
tube  is  about  three-quarters  full,  and  allow  to  stand  till  liquid  is 
clear.  If  Mn  is  present,  the  supernatant  fluid  will  be  a  pink  to 
red  color  due  to  the  formation  of  permanganic  acid,  HMn04. 

N^ole.  —  HCl  or  chlorides,  even  in  small  quantities,  interfere  with  the  reaction; 
hence  it  is  recommended  to  make  the  test  on  the  sulphide.  Reducing  agents  must 
likewise  be  absent.  When  these  precautions  are  observed  the  test  is  a  very  simple 
and  an  extremely  delicate  one. 

MnS04  with  NaOH  gives  flesh-colored  Mn(0H)2,  insoluble 
in  excess  of  reagent  (separation  from  Zn) . 

Upon  fusion  with  a  mixture  of  KXO3  and  XaoCOs,  man- 
ganese salts  produce  green  manganates,  as  Na2Mn04. 

Zinc,  Zn. 

The  Metal.  —  Atomic  weight  65.37.  Occurs  chiefly  as  the 
carbonate,  ZnCOs,  calamine.  A  native  carbonate  of  zinc  is 
also  known  as  smithsonite.  The  sulphide  ZnS  (zinc  blende), 
and  the  siHcate  are  also  natural  sources  of  the  metal. 

Note.  —  The  name  calamine  has  also  been  given  by  Prof.  Dana  of  Yale  to  a 
silicate  of  zinc,  H2Zn2Si06. 

These  ores  of  zinc,  whether  sulphide  or  carbonate,  upon  roast- 
ing in  air  are  converted  into  oxide,  and  the  oxide  is  easily  reduced 
by  carbon  to  metallic  zinc. 

Properties.  —  Melting-point  420°  C.  (burns).  The  metal 
is  bluish  white  in  color,  is  brittle  at  ordinary  temperatures,  but 
malleable  and  ductile  at  140°  to  150°  C.  At  200°  C,  however, 
it  again  becomes  brittle  and  fuses  as  above  stated  at  420°  C. 
At  950°  zinc  boils  and  may  be  distilled;  in  air  it  ultimately 
bums  to  a  white  oxide.  WTienever  zinc  ores  are  sufficiently 
rich  in  the  metal  the  pure  zinc  may  be  separated  by  heating  with 
carbon  out  of  contact  with  the  air  to  a  temperature  considerably 


METALS  OF  GROUP   IV  65 

in  excess  of  its  boiling-point,  when  the  zinc  distills  and  may  be 
condensed. 

Alloy.  —  Zinc  is  of  considerable  importance  from  a  dental 
standpoint,  the  metal  itself  being  used  in  the  manufacture  of 
counter-dies  and  solders;  and,  according  to  Mitchell's  Dental 
Chemistry,  it  may  be  advantageously  used  in  the  proportion  of 
one  to  one  and  live-tenths  per  cent,  in  silver- tin  amalgam  alloys. 
"  It  tends  to  control  shrinkage,  imparts  a  '  buttery  '  plasticity 
to  the  amalgam,  adds  to  the  whiteness  of  the  filling  and  assists 
in  the  maintaining  of  its  color."     See  also  page  124. 

Compounds.  —  The  oxide  of  zinc  combines  with  phosphoric 
acid  and  is  pecuharly  adapted  to  the  preparation  of  dental 
cements.  Zinc  salts  with  alkaHne  carbonates  precipitate  a 
white  basic  carbonate,  Zus  (0H)6  (003)2,  which  is  used  as  a  pig- 
ment in  the  preparation  of  paint  and  also  as  a  source  of  pure 
oxide  of  zinc. 

The  sulphate,  ZnS04,  also  known  as  white  vitriol,  is  per- 
haps the  most  common  salt.  The  chloride  is  a  constituent 
of  many  commercial  Hquid  disinfectants  and  antiseptics.  The 
nitrate  also  is  easily  obtained. 

A  two  or  three  per  cent,  solution  of  any  of  these  soluble  salts 
may  be  used  in  the  following  tests: 

Analytical  Reactions.  —  ZnS04  with  (NH4)2S  gives  a  white 
precipitate  of  ZnS. 

Sulphide  of  zinc  is  the  only  white  sulphide  formed  in  the 
course  of  analysis  of  ordinary  solutions,  but  the  following  white 
precipitates  are  formed :  Sulphide  of  manganese  is  flesh-colored  or 
dirty  white.  Aluminium  hydroxide  resembles  sulphide  of  zinc 
in  appearance  and  is  precipitated  by  (NH4)2S.  Yellow  (NH4)2S 
added  to  an  acid  solution  wiU  precipitate  sulphur,  white,  very 
fine  and  difficult  to  filter  out. 

ZnSOi  with  NaOH  (or  KOH)  gives  a  white  gelatinous  pre- 
cipitate of  zinc  hydrate,  Zn(0H)2,  soluble  in  excess  of  the  reagent 
as  Na2Zn02  (sodium  zincate) . 


66      SALTS  OF   THE  METALS   AND  QUALITATIVE  ANALYSIS 

Note.  —  Colorless  gelatinous  precipitates  in  slight  amounts  may  escape  de- 
tection, as  it  sometimes  takes  careful  observation  to  see  them,  especially  if  the 
laboratory  light  happens  to  be  poor. 

Na2Zn02  with  H2S  or  (NH4)2S  gives  precipitate  of  ZnS. 

From  solution  of  Na2Zn02  the  Zn  may  be  precipitated  as 
Zn(0H)2  by  addition  of  NH4CI,  but  further  addition  of  the 
NH4CI  redissolves  the  precipitate  (distinction  from  Al,  page  57). 

ZnS04  with  K4FeCy6  gives  white  precipitate  of  zinc  ferro- 
cyanide  (Zn2FeCy6),  insoluble  in  NH4OH. 

Note.  —  The  ferrocyanide  and  the  sulphide  are  the  only  two  zinc  salts  not 
soluble  in  NH4OH.     (Prescott  and  Johnson,  page  179.) 

Soluble  zinc  salts,  with  oxalic  acid  or  oxalates,  give  a  pre- 
cipitate of  zinc  oxalate  sufiEiciently  insoluble  in  alcohol  and 
water  to  make  it  available  for  use  in  the  quantitative  separation 
of  zinc  from  dental  alloys.  The  crystals  are  of  characteristic 
form,  which  may  be  recognized  under  a  microscope  (Plate  II, 
Fig.  6,  page  170). 


Analysis  of  Group  IV. 

(Co,  Ni,  Mn,  Zn.) 

(In  the  presence  of  phosphates,  oxalates,  borates,  etc., 
examine  this  group  by  the  scheme  given  on  page  88.) 

To  the  clear  filtrate  from  Group  III  add  (NH4)2S.  A  pre- 
cipitate may  be  NiS,*  CoS,  MnS,  and  ZnS.  Wash  the  precipitate 
and  treat  with  cold  dilute  HCl,  which  will  dissolve  MnS  and  ZnS 
only. 


CoS  and  NiS,  black. 


MnCl2  and  ZnCU  in  solution. 


*  A  black  precipitate  persistently  passing  through  the  paper  is  NiS,  and  some- 
times requires  heating  or  concentrating  before  a  clear  filtrate  can  be  obtained. 


METALS  OF  GROUP  IV  67^ 

Make  a  borax-bead  test  (page  61)  of  the  precipitates  on 
funnel  in  above  figure.  If  a  clear  red-brown  bead  is  obtained, 
Ni  alone  is  present.  If  the  bead  is  blue,  Co  is  present,  Ni  may 
or  may  not  be. 

Separation  of  Cobalt  and  Nickel. 

If  Co  is  present,  dissolve  the  black  precipitate  off  the  paper 
wdth  aqua  regia,  evaporate  in  porcelain  capsule  practically  to 
dryness,  dissolve  in  HoO,  add  excess  of  acetic  acid  and  potassium 
nitrite  (KNO2).  Allow  to  stand  over  night,  when  Co  will 
separate  out  as  a  yellow  crystalline  precipitate  (page  61). 

Filter  and  test  filtrate  for  Ni  with  NaOH,  which  gives  a 
pale-green  precipitate  of  Ni(0H)2  insoluble  in  excess  of  the 
precipitant. 

Separation  of  Manganese  and  Zinc. 

Boil  the  HCl  solution  of  Zn  and  Mn  to  expel  the  H2S,  then 
add  a  decided  excess  of  KOH  or  NaOH  and  allow  to  stand  ten 
minutes  without  heating.  Mn  will  separate  out  as  Mn(0H)2, 
while  Zn  will  remain  in  solution  as  K2Zn02. 


Mn(0H)2. 
KzZnOz. 


Test  precipitate  by  the  red-lead  test  for  Mn,  page  63.  Test 
filtrate  for  Zn  by  adding  H2S  or  a  few  drops  of  (NH4)2S,  which 
will  precipitate  ZnS,  white. 


68      SALTS  OF   THE  METALS  AND  QUALITATIVE  ANALYSIS 

OUTLINE  FOR  ANALYSIS  OF  GROUP  IV. 

To  filtrate  from  Group  III  add  (NH4)2  S.     Filter, 

Ppt.  =  CoS.  NiS.  ZnS.  MnS.    Treat  c  dil.  HCl. 


Residue.  Co  and  Ni.  Make  borax 
bead  test.  Separate  Co  by  means 
of  KNO2  (page  61) 


Sol.  Mn  and  Zn.    Boil  and  heat  c  KOH  or  NaOH. 


Ppt.  Mn(0H)2.     Make  red- 
lead  test 


Sol.     K2Zn02.    Add    H2S : 
ppt.  ZnS  (page  67) 


QUESTIONS  ON  GROUP  IV. 

Why  dissolve  the  MnS  and  ZnS  in  cold  and  dilute  HCl? 

Why  is  it  necessary  to  separate  all  the  Mn  before  testing 
for  Zn? 

If  traces  of  Co  or  Ni  are  dissolved  by  the  HCl,  how  does  it 
affect  the  final  test  for  Zn? 

In  this  analysis  (in  absence  of  phosphates,  etc.)  what  im- 
portant difference  between  the  behavior  of  salts  of  Zn  and  Al? 

Why  is  it  necessary  to  allow  time  for  complete  precipitation 
of  Co  with  KNO2? 

Why  expel  H2S  before  separating  Mn? 

Where  does  this  HoS  come  from? 


CHAPTER   VII. 
METALS   OF   GROUP  V. 

The  Alk.\line  Earths  Ba,  Sr,  Ca,  ]Mg. 

The  common  alkaline  earth  metals  present  similarity  of 
properties  which  aUy  them  more  closely  than  the  metals  of  some 
of  the  pre\ious  analytical  groups.  None  of  the  metals  occur 
free  in  nature.  The  metals  themselves  are  isolated  -vsath  con- 
siderable difficulty,  -vs-ith  the  exception  of  magnesium,  and  they 
all  decompose  water  with  evolution  of  hydrogen;  calcium,  stron- 
tium, and  barium  producing  the  decomposition  at  ordinary  tem- 
peratures; magnesium,  at  high  temperatures  only. 

As  a  group  they  form  insoluble  carbonates,  from  which  carbon 
dioxide  is  easily  driven  off  by  heat,  lea^'ing  the  oxide  of  the  metal. 
This  oxide  unites  with  water,  forming  feebly  soluble  hydroxides. 
The  solutions  of  the  hydroxides  are  alkahne  to  Htmus,  and  are 
used,  to  a  considerable  extent,  in  medicine,  as  antacids. 

There  are  two  other  metals  belonging  to  this  group.  The 
first,  glucinum,  also  caUed  ber\-lHum,  has  an  atomic  weight  of 
9.1.  Soluble  salts  of  glucinum  are  precipitated  by  ammonium 
hydroxide  as  white  and  gelatinous  beryllium  hydroxide.  The 
precipitate  somewhat  resembles  aluminium  hydroxide.  Ammo- 
nium carbonate  also  precipitates  the  hydroxide,  which  is  easily 
soluble  in  excess  of  reagent.  The  solution,  however,  should 
not  be  boiled  as  prolonged  boiling  will  cause  the  berA'Uium 
hydroxide  to  reprecipitate. 

Ber}'llium  oxide  unites  with  phosphoric  acid,  forming  a 
phosphate  similar  in  its  properties  to  the  basic  phosphate  of  zinc, 
and  its  use  is  claimed  by  some  manufacturers  to  be  essential  to 
the  preparation  of  artificial  enamels.     (See  page  138.) 

69 


yo      SALTS  OF   THE   METALS   AND  QUALITATIVE   ANALYSIS 

The  second  rare  metal  belonging  to  this  group  is  radium; 
atomic  weight  226.4.  The  metal  itself  has  not  as  yet  been  iso- 
lated. Its  compounds  are  obtained  from  uraninite  or  pitch- 
blende, a  source  of  uranium.  It  is  bivalent,  and  the  chlorides, 
bromides,  nitrates,  and  hydroxides  have  been  studied. 

Radium  compounds  are  luminous,  and  the  active  emanations 
emitted  by  them  have  been  condensed  at  150°  below  zero  centi- 
grade, forming  new  substances,  among  which  helium  has  been 
identified.  The  discovery  of  this  fact  is  responsible  for  our  new 
conception  of  the  divisibility  or  disintegration  of  what  were 
once  considered  indivisible  atoms,  also  of  the  "  smoke  ring  " 
molecule,  and  the  possible  transmutation  of  the  elements. 

Barium,  Ba. 

Compounds.  —  Barium,  the  next  metal  to  radium  in  this 
group  in  point  of  atomic  weight,  which  is  137.37,  occurs  chiefly 
as  a  sulphate  BaS04,  heavy  spar,  and  BaCOa,  witherite.  Barium 
oxide  may  be  formed  by  heating  the  carbonate  or  nitrate  to  red 
heat.  It  absorbs  oxygen  from  the  air  with  formation  of  the 
binoxide  Ba02.  This  in  turn  is  decomposed,  oxygen  being  given 
off  and  BaO  being  reproduced.  The  barium  oxide  hence  be- 
comes a  source  of  oxygen  of  commercial  importance.  The  cost 
of  producing  oxygen  by  this  method  is  obviously  small. 

The  peroxide  of  barium  is  also  of  particular  importance  to  the 
dentist,  in  that  it  is  an  important  source  of  peroxide  of  hydrogen. 
This  substance  is  considered  more  fully  in  a  chapter  on  mouth 
washes  and  local  anesthetics.     (See  page  180.) 

Barium  hydroxide,  Ba02H2,  slightly  soluble  in  water,  absorbs 
CO2  very  rapidly  and  may  be  used  as  a  test  for  this  gas.  The 
solution  is  known  as  "  Baryta  Water." 

Analytical  Reactions.  —  Use  a  2%  solution  of  the  chloride 
for  tests. 

BaCl2   with  (NH4)2C03   gives  white   precipitate   of  barium 


METALS  OF  GROUP   V  71 

carbonate.  Test  solubility  in  acids.  With  soluble  sulphates 
BaClo  produces  BaS04  insoluble  in  HCl.  (Test  for  sulphates.) 
BaCl2  with  K2Cr207  or  K2Cr04  gives  yellow  precipitate  of 
BaCr04.  Barium  salts  moistened  with  HCl  and  held  on  a  clean 
platinum  wire  give  to  the  colorless  flame  of  the  Bunsen  burner 
a  green  or  yellowish-green  color. 

STRONxroM,  Sr. 

Atomic  weight  87.63.  Occurs  as  the  carbonate,  SrCOa, 
strontianite,  also  as  the  sulphate. 

Strontium  salts  are  used  commercially  in  the  preparation  of 
colored  fires,  strontium  imparting  a  vi\dd  red  color  to  the  flame. 
Strontium  oxalate  crystalHzes  in  practically  the  same  forms  and 
much  more  easily  than  calcium  oxalate. 

Analytical  Reactions.  —  Use  a  3  to  4%  solution  of  the  nitrate 
or  chloride  for  tests. 

Sr(N03)2  ^"ith  (NH4)2C03  gives  white  precipitate  of  SrCOa. 

Sr(N03)2  "^"ith  H2SO4  or  soluble  sulphate  gives  white  pre- 
cipitate of  SrS04,  rather  more  soluble  in  water  and  more  slowly 
formed  than  BaS04. 

A  saturated  solution  of  SrS04  may  be  used  to  test  for  barium 
in  presence  of  Sr  salts. 

Sr(N03)2  ^vith  K2Cr04  gives  precipitate  of  SrCr04,  but  with 
the  acid  chromate  (dichromate)  of  potassium,  K2Cr207,  no 
precipitate  is  formed  except  in  concentrated  solutions. 

Sr(N03)2  \\dth  oxaHc  acid  gives  a  precipitate  of  strontium 
oxalate,  SrC204,  crystalHzing  in  the  so-called  envelop  form  (Plate 
II,  Fig.  3,  page  170).     Salts  of  Sr  color  the  Bunsen  flame  crimson. 

Calcium,  Ca. 

Atomic  weight  40.07.  Calcium  is  widely  distributed  and 
very  abundant,  Hmestone,  chalk,  marble,  and  calc-spar  being 
natural  carbonates;  CaC03,  gj^sum,  and  alabaster  are  sulphates. 


72      SALTS  OF   THE  METALS  AND  QUALITATIVE  ANALYSIS 

Calcium  phosphate  occurs  in  the  mineral  apatite  and  is  also 
a  principal  constituent  of  animal  bones. 

Plaster  of  Paris.  —  Calcium  sulphate  is  of  particular  interest, 
occurring  as  gypsum,  CaS04.2  H2O.  Upon  heating,  the  two 
molecules  of  water  of  crystallization  may  be  driven  off,  leaving 
the  anhydrous  CaS04,  or  plaster  of  Paris,  so  largely  used  in  dental 
laboratories.  If  the  heat  used  is  too  high  a  "  dead  burnt  " 
plaster  results  which  unites  so  slowly  with  water  as  to  be  practi- 
cally useless.  More  careful  dehydration  at  a  lower  temperature 
yields  a  so-called  "  soluble  anhydrite  "  which  absorbs  water 
rapidly.  The  best  plaster  for  dental  purposes  is  neither  of  these, 
but  a  product  which  contains  one  molecule  of  water  to  every  two 
of  calcium  sulphate.  This  is  known  as  the  half  hydrate  and  is 
the  chief  constituent  of  plaster  of  Paris.  This  half  hydrate  has 
a  property  of  setting  with  more  or  less  of  a  fibrous  character 
which  permits  its  use  in  the  formation  of  plaster  casts.  Essig 
states  that  if,  in  the  preparation  of  plaster,  the  heat  is  allowed 
to  exceed  127°  C,  its  afiSnity  for  water  is  impaired  or  destroyed 
and  this  effect  will  not  be  produced.* 

As  plaster  sets,  more  or  less  expansion  takes  place,  and,  if 
spread  upon  glass,  the  mass  usually  rises  slightly  in  the  center, 
producing  a  plate  which  is  somewhat  concave  on  the  under 
surface.  This  tendency  to  expansion  varies  with  different  grades 
of  plaster,  as  may  easily  be  shown  by  a  method  suggested  by 
Dr.  George  H.  Wilson  in  the  Dental  Cosmos  for  August,  1905, 
page  940,  which  consists  simply  of  filling  small  glass  beakers 
with  mixtures  similarly  prepared.  Some  samples  were  found 
to  expand  so  slightly  as  not  to  injure  the  glass,  others  cracked, 
and  some  broke  the  beaker  into  fragments. 

In  the  Dental  Cosmos  for  1908,  page  67,  Dr.  J.  H.  Prothero 
of  Chicago  shows  that  plaster  during  the  first  four  minutes  gives  a 
slight  contraction,  and  is  then  stationary  for  about  forty-five 
seconds.     Then  it  expands  with  increasing  rapidity  till  the  maxi- 

*  American  Text-book  of  Prosthetic  Dentistry. 


METALS  OF  GROUP   V  73- 

miim  movement  attained  is  one-thousandth  of  an  inch  per  minute 
for  about  ten  minutes.  After  half  an  hour  the  movement  prac- 
tically ceases.  The  shghtest  possible  trace  of  potassium  sul- 
phate added  to  the  water  used  in  mixing  and  the  least  possible 
agitation  reduces  both  the  rate  and  the  amount  of  expansion. 

The  method  of  mixing  also  affects  the  amount  of  expansion. 
In  a  valuable  article  on  "  Experiments  in  Plaster  of  Paris  to 
Test  Expansions,"  by  Dr.  Stewart  J.  Spence,  in  Items  of  In- 
terest, 1902,  page  721,  it  is  shown  that  "  not  only  do  different 
plasters  expand  in  differing  degrees,  but  the  same  plaster  expands 
very  differently  according  to  the  stirring  given  it  before  pouring," 
and  that  long  stirring  increases  the  heat  developed,  the  rapidity 
of  setting,  and  the  amount  of  expansion,  but  decreases  the 
strength. 

Various  methods  have  been  prepared  to  overcome  the  diffi- 
culties in  manipulation  of  plaster,  such  as  mixing  the  plaster 
with  alum,  marble-dust,  or  potassium  sulphate.  A  compound 
on  the  market  consists  of  a  mixture  of  plaster  and  Portland 
cement.  A  mixture  which  has  been  very  strongly  recommended 
as  an  investment  preparation  consists  of  two-thirds  plaster  and 
one-third  powdered  pumice-stone. 

Analytical  Reactions.  —  Use  a  3  or  4%  solution  of  CaCl2  for 
tests. 

CaCl2  with  (NH4)2C03  gives  white  precipitate  of  CaCOs, 
easily  soluble  in  acids. 

CaCl2  with  oxalic  acid  or  soluble  oxalates  gives  a  white  pre- 
cipitate of  CaC204,  similar  in  form  to  the  SrC204  but  much  more 
difficult  to  obtain  in  the  crystalhne  condition. 

CaS04  is  not  precipitated  except  from  moderately  concen- 
trated solution. 

A  saturated  solution  of  CaS04  may  be  used  to  test  for  stron- 
tium salts  in  presence  of  Ca. 


74      SALTS   OF   THE  METALS  AND  QUALITATIVE  ANALYSIS 

Magnesium,  Mg. 

The  Metal.  —  Atomic  weight  24.32.  Principal  sources  are 
the  carbonate,  MgCOa,  magnesite,  and  a  double  carbonate, 
CaMg(C03)2,  dolomite.  The  sulphate  MgS04  occurs  in  the 
mineral  kiescrite  in  the  "Stassfurt  deposit."  "  French  chalk  " 
(or  talcum),  soapstone,  and  meerschaum  consist  of  magnesium 
silicate  in  varying  states  of  purity. 

Asbestos  is  a  double  silicate  of  magnesium  and  calcium. 

Properties.  — -  Magnesium  is  a  silver  white  metal  occurring 
in  trade  as  ribbon  or  powder.  It  burns  easily  in  air,  forming 
MgO  and  traces  of  MgsNo  and  producing  a  white  light  which  is 
used  in  photography.  It  is  a  Hght  metal  having  a  specific 
gravity  of  1.75. 

Alloys.  —  For  the  alloy  with  aluminium,  see  page  56.  The 
amalgam  alloys  are  not  practical  as  they  heat  and  swell  in  a  man- 
ner which  renders  them  practically  useless. 

Compounds.  —  Epsom  salt,  or  magnesium  sulphate,  occurs 
as  a  constituent  of  laxative  waters.  The  crystalUzed  salt, 
MgS04.7  H2O  resembles  oxalic  acid  in  appearance,  and  has  been 
mistaken  in  several  instances  for  the  poisonous  acid. 

Magnesium  carbonate  is  used  in  pharmacy  in  two  forms; 
viz.,  the  Hght  and  the  heavy.  These  are  produced  by  precipi- 
tating dilute  or  concentrated  solution  of  magnesium  sulphate 
with  sodium  carbonate. 

The  light  and  heavy  magnesium  oxides  are  produced  by 
calcination  of  the  Ught  or  heavy  carbonates.  Magnesium  salts 
are  quite  generally  distributed  in  the  human  system,  but  in 
small  quantities.  They  occur  in  the  bones,  the  teeth,  and  the 
various  body  fluids. 

Analytical  Reactions.  —  A  five  per  cent,  solution  of  the 
sulphate  or  nitrate  may  be  used  in  the  following  tests: 

Magnesium  salts  with  (NH4)oC03  give  a  white  precipitate 
of  basic  carbonate  of  variable  composition.     This  precipitate 


METALS  OF  GROUP   V 


'75 


forms  very  slowly  in  dilute  solution,  and  in  the  presence  of 
NH4CI  the  formation  of  soluble  double  salts  prevents  the  pre- 
cipitation altogether. 

MgCl2  with  Na2HP04  gives  in  fairly  concentrated  solution 
a  white  precipitate  of  MgHP04.  In  presence  of  NH4CI  and 
NH4OH  the  alkaHne  phosphates  precipitate  magnesium-am- 
monium-phosphate, MgNH4P04.6  H2O,  even  from  very  dilute 
solution  (Plate  IV,  Fig.  2). 

In  case  the  precipitate  has  formed  very  slowly,  it  may  separ- 
ate as  small,  almost  transparent,  crystals  clinging  to  the  sides 
of  the  beaker. 

Ammonium  oxalate  does  not  precipitate  magnesium  solutions. 

Analysis  of  Group  V. 

(Ba,  Sr,  Ca,  Mg.) 

To  the  filtrate  from  Group  IV  containing  NH4CI  and  NH4OH, 

add  (NH4)2C03.  (If  NH4CI  and  NH4OH  are  not  present,  add 
10  c.c.  of  NH4CI  solution  and  NH4OH  till  strongly  alkahne  before 
proceeding  with  the  analysis.)  Ba,  Sr,  and  Ca  will  be  pre- 
cipitated as  carbonates;  Mg  will  be  held  in  solution  by  the 
ammonium  chloride.     Filter. 


Ca,  Ba,  Sr  carbonates. 


Mg  and  metals  of  Group  VI. 


Test  the  filtrate  for  Mg  by  adding  Na2HP04,  when  a  white 
crystalHne  precipitate  is  NH4MgP04.6  II2O. 

To  the  carbonates  on  the  paper  add  dilute  acetic  acid,  which 
will  dissolve  the  precipitate,  forming  acetates  of  the  three  metals. 


76      SALTS  OF   THE  METALS  AND  QUALITATIVE  ANALYSIS 

Take  a  portion  of  the  acetate  solution  in  a  test-tube  and  make 
a  preliminaiy  test  for  Ba  by  adding  acid  chroma te  of  potas- 
sium (K2Cr207).     A  yellowish  precipitate  will  be  BaCr04. 

If  Ba  is  present,  add  K2Cr207  to  the  whole  of  the  solution 
and  filter  out  the  BaCr04. 


BaCr04. 


Sr  and  Ca  acetates,  K2Cr207,  etc. 


It  is  desirable  to  remove  the  excess  of  bichromate  from  the 
filtrate  before  testing  for  Ca  and  Sr.*  To  do  this  add  NH4OH 
till  alkaline;  then  (XH4)2C03  will  precipitate  SrCOs  and  CaCOa. 
Filter  and  dissolve  off  the  paper  with  acetic  acid  as  before. 


CaCOs  and  SrCOs,  which  when  treated  with  acetic 


acid,  will  give  a  solution  of  the  acetates  of  Ca  and  Sr. 


Reserve  about  one-fourth  of  this  acetate  solution.  To  the 
remainder  add  dilute  K2SO4  solution,  which  will  precipitate 
SrS04.  (If  only  shght  amounts  of  Sr  are  present,  it  may  take 
some  time  to  complete  the  precipitation.     If  a  large  amount 

*  The  object  of  removing  the  K2Cr207  is  to  furnish  a  colorless  solution  wherein 
the  Sr  or  Ca  precipitates  may  be  more  clearly  discerned.  It  is  not  absolutely 
necessary  and,  in  case  the  amount  of  Sr  and  Ca  is  probably  slight,  might  be  omitted, 
as  the  operation  is  always  attended  with  some  loss. 


METALS  OF  GROUP   V 


77 


of  Ca   is   present,  some    CaSO^  may  also    be  thrown  down.) 
Filter. 


SrSOi. 


Ca(C2H302)2orCaS04. 


Test  filtrate  for  Ca  by  adding  ammonium  oxalate,  which  will 
precipitate  calcium  oxalate,  white. 

If  there  is  any  question  about  the  precipitate  thrown  out  by 
K2SO4  being  Sr,  make  confirmatory  test  on  reserved  portion, 
either  by  flame  test  (page  71),  or  by  adding  CaS04,  and  allowing 
to  stand  twelve  hours.  CaS04  A\all  precipitate  Sr  as  SrSO^,  but 
of  course  cannot  precipitate  Ca. 

QUESTIONS  ON  GROUP   V. 
Why  add  NH4CI  before  precipitating  the  group  with  (NH4)2 


Why  dissolve  the  precipitated  carbonates  in  acetic  acid 
rather  than  HCl? 

WTiy  use  the  acid  chromate  of  potassium  (KoCroOy)  in  testing 
for  Ba  rather  than  the  neutral  chromate  (K2Cr04)? 

WTiy  precipitate  Sr  and  Ca  after  separation  of  Ba  vnib. 
KoCrodr? 

ouTLixE  sche:me  for  an.\lysis  of  group  V 

To  clear  filtrate  from  Group  IV  add  (XH4)2C03. 


Precipilate=Ba.,  Sr,  and 
cipitate  Ba. 

Ca.    Add  K2Crz07,  if  necessary  to  pre- 

Solulion=Ug.     Test    for    Mg 
with    Na2HP04    (page   75). 

Precipit<jU=Ba.CTOi. 

Soluiion  =  Sr  and  Ca.     Reprecipi- 
tate  Sr  or  Ca  with  (NH4).COi. 
Dissolve   in   HA.     Remove   Sr 
with   K0SO4  and   alcohol,  and 
test  filtrate  tor  Ca  with  (NHi), 
Q.Oj  (page  73)  • 

CHAPTER  VIII. 
METALS    OF    GROUP   VI. 

The  Alkaline  Metals,  K,  Na,  NH,  Li. 

PoTASsroM,  sodium,  and  the  hypothetical  "  metal "  ammo- 
nium are  the  bases  of  a  very  large  number  of  salts  used  in  the 
arts  and  sciences. 

As  a  class  the  metals  may  be  distinguished  from  the  alkaline 
earths  by  the  ready  solubility  of  their  hydrates  and  carbonates. 
The  hydrates  of  the  alkaline  earths  are  only  sparingly  soluble, 
and  their  carbonates  are  insoluble. 

-•   The  salts  of  hthium  are  also  soluble,  but  are  used  in  relatively 
smaU  amounts. 

These  bases  are  not  precipitated  by  any  group  reagent  and 
must  be  detected  by  individual  tests. 

Potassium,  K  (Kalium). 

The  Metal.  —  Atomic  weight  39.1.  Occurs  as  carbonate  in 
wood  ashes,  as  nitrate  in  the  "  niter  beds  "  of  India,  etc.,  as 
chloride  from  the  Stassfurt  deposit  in  the  Province  of  Saxony, 
Prussia,  as  the  mineral  sylvite,  also  in  the  double  chloride  of 
magnesium  and  potassium  (carnallite) . 

Properties.  —  Melting-point  62.5°.  Potassium  is  a  silver 
white  metal.  It  decomposes  water  at  ordinary  temperatures 
evolving  enough  heat  to  ignite  the  Hberated  hydrogen. 

Compounds.  —  The  salts  of  potassium  are  generally  soluble 
in  water.  Among  the  more  important  compounds  is  the  hy- 
droxide KOH.  This  is  used  very  largely  as  a  starting  point  in 
the  preparation  of  many  of  the  medicinal  salts  of  potassium.     It 

78 


METALS  OF  GROUP   VI  fg 

may  be  made  by  treating  potassium  carbonate  with  slaked  lime, 
according  to  the  following  reaction: 

CaOaHz  +  K2CO3  =  CaCOa  +  2  KOH. 

The  carbonate  obtained  from  wood  ashes  is  known  as  "salts 
of  tartar,"  and  in  the  impure  form  as  pearl  ash.  Potassium  car- 
bonate is  also  made  in  large  quantities  from  the  native  chloride 
found  in  the  Stassfurt  deposit. 

The  bicarbonate  KHCO3,  or  saleratus,  may  be  obtained  by 
saturating  the  carbonate  with  CO2. 

K2CO3  +  CO2  +  H2O  =  2  KHCO3. 

This  salt,  used  in  cooking,  proves  more  or  less  irritating,  and  has 
been  practically  replaced  by  the  corresponding  sodium  salt, 
NaHCOs  or  "  cooking  soda." 

Potassium  nitrate,  KNO3,  also  called  niter  and  saltpeter,  is 
used  in  medicine  as  a  diuretic.  It  gives  off  oxygen  easily,  and 
is  consequently  a  good  oxidizing  agent,  and  as  such  is  a  con- 
stituent of  fireworks,  gunpowder,  etc. 

KNO3  may  be  prepared  from  the  cheaper  sodium  nitrate  by 
double  decomposition  with  potassium  chloride. 

NaN03  +  KCl  =  KNO3  +  NaGl. 

Potassium  bromide,  used  as  a  sedative,  may  be  prepared  by 
treating  caustic  potash,  KOH,  with  bromine. 

6  Br  +  6  KOH  =  5  KBr  +  3  H>0  +  KBr03. 

The  bromate,  KBrOs,  is  separated  by  crystallization. 

Potassium  iodide  may  be  made  in  a  similar  manner  by  sub- 
stituting iodine  for  the  bromine.  Potassium  iodide  is  very 
soluble,  being  dissolved  in  less  than  its  own  weight  of  water. 
In  the  laboratory  potassium  iodide  is  used  as  a  solvent  for  iodine, 
and  as  a  reagent. 

Potassium  cyanide,  KCN,  an  extremely  poisonous  compound, 
is  used  by  jewelers  for  cleaning  silver,  etc.,  and  in  the  arts  for 
the  preparation  of  double  salts  used  in  electro-plating.     It  is 


8o     SALTS  OF  THE  METALS  AND  QUALITATIVE  ANALYSIS 

decomposed  by  CO2,  forming  K2CO3  and  liberating  hydrocyanic 
acid. 

Potassium  ferrocyanide  and  ferricyanide  are  considered  under 
cyanogen  compounds  in  Chapter  XXV. 

Potassium  chlorate  may  be  prepared  by  treating  a  hot  solution 
of  the  hydroxide  with  chlorine  gas.  The  reaction  is  the  same  as 
that  given  for  the  preparation  of  the  bromide,  and  results  in  five 
molecules  of  the  potassium  chloride  to  one  of  the  chlorate. 

Potassium  sulphide,  K2S,  is  soluble  in  water  and,  in  common 
with  other  alkaline  sulphides,  is  a  solvent  for  sulphur,  thereby 
forming  a  number  of  polysulphides. 

The  pentasulphide,  K2S5,  is  known  as  "Hver  of  sulphur"  or 
sulphuret  of  potassium. 

Potassium  platinic  chloride,  KoPtCle,  and  potassium  acid 
tartrate,  KHC4H4O6,  are  only  sparingly  soluble  and  may  be 
precipitated  by  addition  to  the  solution  of  an  equal  volume  of 
alcohol,  in  which  they  are  quite  insoluble. 

The  potassium  acid  tartrate,  or  bitartrate,  is  also  called 
cream  of  tartar,  and  is  used  in  the  manufacture  of  baking  powder. 
This  salt  separates  from  wine  vats,  it  being  precipitated  by  the 
alcohol  produced  during  the  process  of  fermentation  of  the  grape 
juice.    In  this  impure  form  it  is  known  as  argols,or  crude  tartar. 

Analytical  Reactions.  —  The  presence  of  potassium  salts 
may  be  detected  spectroscopically  or  by  the  violet  color  given 
to  the  flame  observed  through  blue  glass.  Make  comparative 
tests  with  known  solutions  of  sodium  and  potassium  salts,  using 
blue  glass  of  sufficient  thickness  to  obscure  the  yellow  (Na)  ray. 

Note.  —  In  making  the  flame  test  the  best  results  are  obtained  by  evaporating 
a  little  of  the  original  solution  to  drjoiess,  moistening  with  HCl  and  then  taking 
up  on  a  loop  of  clean  platinum  wire. 

The  platinic  chloride  test  may  be  made  as  follows: 
Add  a  few  drops  of  HCl  to  a  Uttle  of  the  solution,  then  evapo- 
rate to  dryness.     Keep  at  a  low  red  heat  till  all  ammonium 
salts  have  been  driven  off,  cool,  and  take  up  in  a  little  (not 


METALS  OF  GROUP   VI  8 1 

more  than  5  c.c.)  distilled  water.  Add  a  few  drops  of  H2PtCl6 
and  about  5  c.c.  of  alcohol.  Set  aside  for  some  time.  K2PtCl6, 
yellow,  will  crystallize  out  recognizable  under  the  microscope 
(Plate  III,  Fig.  3). 

Sodium,  Na  (Natrium). 

The  Metal.  —  Atomic  weight  23.0.  It  occurs  principally  as 
chloride  in  sea-water  and  in  mineral  deposits,  and  to  a  lesser  ex- 
tent as  nitrate,  Chih  saltpeter,  and  as  cryoHte,  the  double  fluor- 
ide of  aluminium  and  sodium,  (NasAlFe),  found  in  Greenland. 

Properties.  —  Melting-point  95.6°.  Sodium  is  a  shiny  metal 
of  cheese-hke  consistency,  easily  cut  with  a  knife.  It  tarnishes 
quickly  in  the  air,  with  the  formation  of  the  hydroxide.  Sodium, 
and  potassium  also,  can  be  distilled  in  atmospheres  which  do 
not  affect  the  metal. 

Compounds.  —  Sodium  peroxide,  or  dioxide,  Na202,  may  be 
prepared  by  simply  heating  metallic  sodium  in  dry  air.  It  is  a 
yellowish  white  powder  used  somewhat  in  dental  practice  for 
the  preparation  of  alkaline  solutions  of  H2O2 : 

Na202  -f  2  HoO  =  2  NaOH  +  H.Oo. 

The  alkaHne  peroxide  is  much  more  efficient  as  a  bleaching  agent 
than  the  neutral  or  acid  preparations. 

Sodium  hydroxide,  NaOH,  is  found  in  trade  in  several  forms. 
The  stick  "  caustic  soda,  "  used  in  chemical  laboratories,  contains 
anywhere  from  five  to  thirty  per  cent,  of  water.  In  a  powder 
form,  less  pure  than  the  above,  it  is  known  as  "  concentrated 
lye,"  Babbitt's  potash,  etc.,  and  is  used  for  cleaning,  and  in  the 
manufacture  of  soap.  Sodium  hydroxide  is  caustic  or  escharotic 
in  its  action  upon  animal  tissue.  It  may  be  made  experimentally 
by  experiment  No.  49,  page  376. 

Sodium  carbonate,  NaoCOs,  crystallizes  with  ten  molecules 
of  water.  In  this  form  it  is  known  as  "  sal  soda,"  or  washing 
soda.     It  is  used  as  a  starting  point  in  the  manufacture  of  other 


82      SALTS  OF   THE   METALS  AND  QUALITATIVE   ANALYSIS 

sodium  salts.  Sodium  carbonate  is  produced  from  sodium  chlo- 
ride by  the  Le  Blanc  process,  in  which  the  following  reactions  are 
involved : 

(i)  2  NaCl  +  H2SO4  =  Na2S04  +  2  HCl. 

(2)  Na2S04  +  2  C  =  Na.S  +  2  COo. 

(3)  NasS  +  CaCOs  =  Na^COg  +  CaS. 

The  last  two  reactions  are  combined  in  the  actual  process  of 
manufacture,  and  the  mixture  of  sodium  sulphate,  carbon,  and 
calcium  carbonate  are  heated  together  with  the  resulting  forma- 
tion of  "  black  ash  "  from  which  is  produced  pure  sodium  car- 
bonate. 

More  recent  processes  are  the  Solvay  or  ammonia  process, 
depending  on  the  following  reaction: 

NaCl  +  NH3  +  CO2  +  H2O  =  NaHCOs  +  NH4CI, 

and  the  cryolite  process  in  which  the  source  of  the  sodium  is  the 
double  fluoride  of  sodium  and  aluminum,  NasAlFe.  By  this 
process  the  cryolite  is  heated  with  Hme,  forming  calcium  fluoride 
and  sodium  aluminate. 

NasAlFe  +  3  CaO  =  3  CaFo  +  Na3A103. 

Note.  —  According  to  Remsen  the  sodium  aluminate  probably  consists  of  a 
variety  similar  in  composition  to  the  potassium  aluminate  given  on  page  57 
(NaA102  and  Na20  until  water  is  added) . 

Sodium  bicarbonate,  NaHCOa,  also  called  cooking  soda,  is 
largely  used  like  "  saleratus  "  (KHCO3)  as  a  source  of  carbon 
dioxide  in  the  leavening  or  aerating  of  bread. 

Sodium  bicarbonate  is  hydrolyzed  by  water,  i.e.,  it  dissociates 
in  solution  forming  sodium  hydroxide  and  carbonic  acid.  The 
carbonic  acid  is  a  weak  acid  furnishing  very  few  hydrogen  ions, 
while  the  hydroxide  is  a  strong  base.  It  follows  that  the  reaction 
of  such  a  solution  is  alkaline  to  Htmus,  although  the  salt  answers 
to  our  definition  of  an  acid  salt.     This  is  true  of  sodium  car- 


METALS  OF  GROUP   VI  d>:i 

bonale  (the  products  of  hydrolysis  being  NaOH  and  NaHCOs), 
and  in  a  similar  manner  of  corresponding  potassium  salts. 

Sodium  chloride  NaCl,  common  salt,  exists  in  sea-water  to 
the  extent  of  2.7%,  and  is,  to  some  extent,  obtained  from  this 
source,  although  the  greater  amount  is  produced  by  the  salt 
mines.  Salt  is  a  constituent  of  all  of  the  body  fluids,  and  can  be 
easily  obtained  as  cubical  crystals  by  the  evaporation  of  urine  or 
of  dialyzed  saliva. 

Physiological,  or  normal  salt  solution,  contains  about  0.7%  of 
sodium  chloride,  and  has  practically  the  same  osmotic  pressure 
as  blood. 

The  term  "  physiological  "  is  to  be  preferred  to  the  term 
"  normal,''  as  normal  salt  solution  is  also  properly  appUed  to  a 
solution  used  in  volumetric  analysis  containing  exactly  5.85%  of 
sodium  chloride  (see  page  159). 

Sodium  nitrate,  NaNOs,  Chili  saltpeter,  is  valuable  as  a  fer- 
tilizer, but  too  hygroscopic  to  be  used  in  the  same  way  as  potas- 
sium nitrate,  in  the  preparation  of  gunpowder,  fireworks,  etc. 

Sodium  phosphate,  trisodic  phosphate,  NasPO^,  is  a  crystal- 
line salt,  soluble  in  water,  but  of  slight  interest  in  Dental  Chem- 
istry. It  is  easily  decomposed  by  CO;;,  forming  NaoHPO^  and 
Nao'cOs. 

2  NasPOi  +  HoO  +  CO2  =  2  NaoHP04  +  Xa.COs. 

The  disodic  phosphate,  Na2HP04,  also  called  neutral  or 
orthosodium  phosphate,  is  the  sodium  phosphate  of  the  Pharma- 
copoeia. It  is  faintly  alkahne  in  reaction,  and  exists  in  the  body 
fluids  generally.  The  alkahne  reaction  (to  litmus)  of  saliva  is, 
in  part,  due  to  its  presence.     . 

The  acid,  or  monobasic  sodium  phosphate,  NaHoPO^,  is  a 
translucent  crystalhne  salt  found  to  some  extent  in  the  body 
fluids,  particularly  the  urine,  to  the  acidity  of  which  it  is  probably 
a  contributing  factor,  although  to  a  much  less  extent  than  was 
formally  supposed. 


84      SALTS   OF    THE   METALS   AND  QUALITATIVE   ANALYSIS 

Sodium  potassium  tartrate,  KNaC4H406,  Rochelle  salt,  is 
used  in  medicine  as  a  mild  laxative.  It  is  the  product  of  the 
double  decomposition  incident  to  raising  bread  with  "  cream  of 
tartar  and  soda." 

KHC4H4O6  +  NaHCOs  =  KNaC4H406  +  CO..  +  H.O. 

Sodium  sulphate  crystallized  with  ten  molecules  of  water 
(Na2S04.io  H2O)  is  known  as  Glauber's  salt. 

Analytical  Reactions.  —  Na  may  be  detected  by  the  use  of  the 
spectroscope  or  by  the  persistence  of  the  yellow  flame  obtained 
with  a  clean  platinum  wire  and  a  colorless  Bunsen  flame.  ]Make 
a  comparative  test  with  small  amount  of  known  sodium  salt. 

Sodium  salts  are  soluble  with 
only  a  very  few  exceptions.  The 
pyroantimonate,  NaoHoSboOy,  may 
be  precipitated  in  the  cold  by  a 
freshly  prepared  solution  of  potas- 
sium pyroantimonate.  (Prescott 
and  Johnson,  page  228.) 

From  a  solution  stronger  than 
3%  and  nearly  neutral  the  double 
acetate    of    uranyl    and    sodium 

Fig.  6.  Uranyl  Sodium  Acetate.  (NaC2H302,U02(C2H302)2)  may  be 
precipitated.  (Fig.  6.)  As  triple  crystalline  acetates  may  also 
be  formed  with  Mg,  Cu,  Fe,  Ni,  and  Co,  it  is  recommended  to 
first  precipitate  the  bases  of  the  first  five  groups  and  drive  off 
ammonium  salts,  as  in  the  test  for  K  with  H2PtCl6.* 

LiTHItJM,    Li. 

Atomic  weight  6.94.  The  carbonate,  citrate,  bromide,  and 
chloride  are  used  in  medicine. 

The  value  of  lithium  salts  as  uric  acid  solvents  is  question- 
able, because  of  the  insolubiUty  of  the  phosphate  (page  242). 

*  Behrens's  Manual  of  Microchemical  Analysis,  page  32. 


METALS  OF  GROUP    VI  85 

The  presence  of  lithium  is  easily  shown  after  the  precipitation 
of  strontium  by  the  intense  carmine  color  given  to  the  Bunsen 
flame. 

The  spectroscope  furnishes  a  very  dehcate  and  positive  test 
for  this  element. 

Ammonium,  NH4. 

Ammonia  is  obtained  in  large  part  from  the  ammoniacal 
liquor  of  the  gas  works,  where  illuminating  gas  is  made  by  the 
distillation  of  coal.  The  Hquor,  charged  with  ammonia,  is 
treated  with  hydrochloric  or  sulphuric  acid,  thus  producing  an 
impure  salt  which  is  subsequently  purified  or  used  as  a  source 
of  NH3  in  the  preparation  of  pure  ammonium  compounds. 

(NH4)2S04  +  CaOsHa  =  CaSOi  +  2  NH3  +  2  H2O. 

Compounds.  —  Ammonium   hydroxide,  NH4OH,  has   never 
been  separated  as  such,  free  from  water.     It  undoubtedly  ex- 
ists, however,  in  aqueous  solutions  of  ammonia  gas. 
NH3  +  H2O  =  NH4OH. 

The  negative  hydroxyl  ions  of  this  ammonium  base  are  not 
separated  by  dissociation  to  the  same  degree  as  those  of  potas- 
sium hydroxide  in  solution;  hence,  it  is  a  weaker  base. 

Aqua  ammonia  of  the  pharmacopeia  contains  10%  NH3. 
The  "  stronger  water  of  ammonia  "  contains  28%  of  the  gas, 
which  is  about  as  strong  a  solution  as  it  is  safe  to  make  for 
shipment,  and  containers  should  never  be  more  than  four- 
fifths  full.  The  28%  solutionis  referred  to  as  26°  ammonia,  the 
degree  indicating  the  specific  gravity  as  taken  by  the  Baume 
.^lydrometer. 

Ammonium  carbonate  exists  in  solution.  The  salt  used  in 
medicine  under  this  name  is  really  a  mixture  of  ammonium 
bicarbonate,  NH4HCO3,  and  the  carbamate,  NH4NH2CO2. 

This  salt  gives  off  NH3  gas,  and  moistened  with  ammonia 
water  and  perfumed  constitutes  "  smelling  salts." 


86      SALTS  OF  THE  METALS  AND  QUALITATIVE  ANALYSIS 

Ammonium  chloride,  sal  ammoniac  (NH4CI),  white,  crystal- 
line, is  made  by  neutralizing  NH4OH  with  hydrochloric  acid. 
Ammonium  chloride  will  subhme  unchanged.  It  is  freely  sol- 
uble in  water,  its  solution  acts  as  an  electrolyte  and  will 
dissolve  metals  from  an  alloy.  If  a  silver  spoon  or  a  ten  cent 
piece  is  allowed  to  remain  for  ten  or  twelve  hours  in  a  dilute 
solution  of  ammonium  chloride,  an  appreciable  amount  of  copper 
will  pass  into  solution,  coloring  it  blue  or  green,  according  to  the 
concentration  of  the  copper  solution.  It  also  dissolves  some 
metallic  oxides,  as  zinc  oxide. 

As  saHva  is  known  to  contain  considerable  NH4CI,  the  above 
facts  should  be  studied  carefully  in  considering  the  action  of 
saliva  on  substances  used  for  filHng  teeth,  although  the  solvent 
action  of  NII4CI  in  saliva  is  nothing  like  what  it  is  in  water. 

Ammonium  nitrate,  NH4NO3,  crystalHzes  in  large  six-sided 
prisms  without  water  of  crystallization.  It  is  very  soluble  in 
water.  It  melts  at  165°  C.  Heated  to  210°  C,  it  decomposes 
into  nitrous  oxide  and  water.  Above  250°  C,  other  oxides 
of  nitrogen  are  produced,  so  in  the  preparation  of  nitrous  oxide 
for  dental  anesthesia,  care  should  be  taken  to  keep  the  tem- 
perature of  the  reaction  between  these  Hmits. 

Ammonium  acetate,  NH4C2H3O2.  A  solution  of  this  salt, 
containing  about  7%,  is  used  in  medicine  as  a  diaphoretic. 
The  solution  is  also  known  as  Spirit  of  Mindererus.  In  analyti- 
cal chemistry,  it  is  used  as  a  solvent  for  lead  sulphate. 

Ammonium  sulphate,  (NH4)2S04,  is  a  white  crystalline  salt 
soluble  in  water,  not  used  medicinally,  but  largely  used  as  a 
reagent  in  physiological  chemistry.  It  melts  at  140°  C,  and 
at  a  higher  temperature  it  decomposes. 

Ammonium  sulphide,  (NH4)2S,isused  as  a  solvent a.nd  reagent. 
It  may  be  prepared  by  saturating  ammonia  water,  NH4OH, 
with  H2S,  then  adding  an  equal  volume  of  ammonia  water: 

NH4OH  +  H2S  =  NH4SH  +  HoO, 
and  NH4SH  +  NII4OH  =  (NIl4)2S  -F  H2O. 


METALS  OF  GROUP   VI  87- 

A  polysulphide,  made  by  dissolving  sulphur  in  (NH4)2S  is 
the  reagent  used  in  dissolving  the  sulphides  of  Group  II  {b)  and 
in  precipitating  the  zinc  group. 

Ammonium  phosphates.  Ammonium,  like  other  univalent 
bases,  is  capable  of  forming,  with  phosphoric  acid,  three  differ- 
ent salts.  (NH4)3P04  is  very  unstable.  The  diammonium  phos- 
phate has  been  used,  to  a  slight  extent,  in  medicine  (Br.  P.)  and 
has  been  shown  to  be  an  energetic  activator  of  lactic  acid  organ- 
isms.* 

The  importance  of  this  fact,  in  relation  to  dental  caries,  has 
yet  to  be  demonstrated. 

Microcosmic  salt  is  a  name  given  to  a  double  ammonium 
sodium  phosphate  (NH4NaHP04.4H20)  used  in  blowpipe 
analysis. 

Analytical  Reactions.  —  Ammonium  salts  are  generally  sol- 
uble. H2PtCl6  precipitates  the  double  chloride  (NH4)2PtCl6, 
similar  in  appearance  and  crystalline  form  to  the  corresponding 
potassium  salt  (Plate  III,  Figs.  1-3). 

Ammonium  salts  are  most  easily  detected  by  the  evolution 
of  ammonia  gas  (NH3)  whenever  they  are  heated  with  fixed 
alkaU,  NaOH  or  KOH. 

The  test  may  be  made  upon  the  original  solution  by  boiling 
in  a  test-tube  with  a  Uttle  10%  NaOH,  and  the  escaping  NH3 
may  be  detected  by  the  odor  or,  better,  by  suspending  in  the 
upper  part  of  the  tube  a  piece  of  moistened  red  litmus  paper, 
which  is  promptly  turned  blue  by  the  "  volatile  alkali."  The 
litmus-paper  test  is  more  deHcate  than  the  odor  test.  Care 
should  be  taken  that  the  paper  does  not  touch  the  sides  of  the 
tube,  as  it  may  come  in  contact  with  traces  of  NaOH. 

Many  ammonium  solutions  giye  off  NH3  gas  without  the  aid 
of  any  fixed  alkaH.  Common  examples  are  the  carbonate,  acid 
carbonate,  hydrate,  sulphide,  and  sulph-hydrate. 

*  Dr.  Percy  Howe  in  Dental  Cosmos.  Jan.,  1912. 


88      SALTS  OF   THE  METALS  AND  QUALITATIVE  ANALYSIS 

QUESTIONS  ON  GROUP   VI. 

Why  use  alcohol  in  the  precipitation  of  ammonium  or  potas- 
sium as  double  chloride  with  platinum? 

Why  are  the  flame  tests  preferably  made  with  chlorides  of 
the  metals? 

Why  is  ammonia  called  the  volatile  alkaU,  and  what  are  the 
fixed  alkaHs  from  which  it  is  thus  distinguished? 

Analysis  of  Groups  III,  IV,  and  V. 

(WTien  phosphates,  borates,  or  oxalates  are  present.) 

To  the  filtrate  from  Group  II  add  NH4CI  and  NH4OH  in 
slight  excess.  Heat  to  boiling  and  add  (NH4)2S  slowly  (always 
keeping  the  solution  at  the  boiling-point)  until  precipitation  is 
complete.  Filter  as  rapidly  as  possible  and  wash  with  hot  water, 
adding  occasionally  a  Httle  (NH4)2S. 

The  filtrate,  which  may  contain  the  barium  and  potassium 
groups,  must  be  concentrated  by  evaporation,  filtered  if  neces- 
sary, and  set  aside.*  The  precipitate  may  contain  MnS,  ZnS, 
CoS,  NiS,  FeS,  A1(0H)3,  and  Cr(0H)3  with  phosphates  or 
oxalates  soluble  in  acids  only.  The  color  of  the  precipitate 
will  give  some  indication  of  what  is  present.  Test  the  pre- 
cipitate for  Mn  by  fusing  a  part  with  KNO3  and  Na2C03. 

Treat  the  precipitate  with  cold  dilute  HCl  in  which  CoS  and 
NiS  alone  are  insoluble.  Filter.  Treat  insoluble  residue  for 
Co  and  Ni  according  to  directions  on  page  67. 

The  HCl  solution,  which  may  contain  Mn,  Zn,  Fe,  Cr,  and 
Al  as  chlorides,  and  phosphates  and  oxalates  soluble  in  acids,  and 
which  is  green  or  violet  if  much  Cr  is  present,  is  boiled  with  a 
few  drops  of  HNO3  until  all  the  H2S  is  expelled.     , 

Test  a  stnall  portion  of  the  solution  for  Fe  exactly  as  'in 

*  If  Ni  is  present,  the  filtrate  is  frequently  brown  or  black,  since  NiS  is  some- 
what soluble  in  an  excess  of  (NH4)2S,  especially  if  much  NH4OH  is  present.  The 
NiS  may  be  precipitated,  after  evaporation,  by  acidifjdng  with  HCl. 


METALS  OF  GROUP   VI 


89. 


analysis  of  Group  III  given  on  page  59.     Of  the  remainder  of 
the  solution  take  about  one-third,  and  add  dilute  H2SO4. 

A  white  precipitate  may  contain  BaS04,  SrS04,  and  possibly 
CaS04.  Filter,  wash  precipitate,  and  fuse  with  a  mixture  of 
NasCOs  and  K2CO3. 

Note.  —  The  mixture  of  the  two  carbonates  in  molecular  proportions  fuses  at 
a  lower  temperature  than  either  salt  alone. 

Filter  and  wash  the  carbonates  thus  formed,  dissolve  them  in 
acetic  acid  and  examine  this  solution  for  Ba,'  Sr,  and  Ca  as  di- 
rected under  the  Ba  group.  To  the  filtrate  from  the  precipitate 
produced  by  H2SO4,  or  to  the  solution  in  which  H2SO4  has  failed 
to  give  a  precipitate,  add  three  times  its  volume  of  alcohol; 
Ca,  if  present,  is  precipitated  as  white  CaS04,  and  its  presence 
may  be  confirmed  by  dissolving  the  precipitate  in  water  and 
adding  (NH4)2C204,  which  precipitates  CaC204,  white. 

To  the  rest  of  the  HCl  solution  add  ferric  chloride,  carefully, 
till  a  drop  of  the  solution  gives,  when  mixed  with  a  drop  of  am- 
monic  hydrate,  a  yellowish  precipitate.  To  the  solution  add 
Na2C03  or  K2CO3  till  the  acid  is  nearly  neutralized,  then  add 
excess  of  freshly  precipitated  BaCOs,  and  allow  to  stand  over 
night.     Filter. 


Cr  and  Al  as  hydrates, 
drate  and  BaCOs.) 


(Fe  as  phosphate  or  hy- 


MnCl2,  ZnCU,  and  possibly  members  of  Group  V. 


Transfer  the  precipitate  to  a  small  beaker  and  boil  for  soine 
time  with  NaOH  or  KOH.  The  Al  will  be  converted  into  the 
aluminate  KAIO2.  The  phosphate  will  be  more  or  less  com- 
pletely changed  to  potassium  or  sodium  phosphate.     Filter, 


90      SALTS  OF   THE  METALS  AND  QUALITATIVE  ANALYSIS 


Cr(0H)3,  BaCO,  etc. 
KAIO2  and  NaaHPOi. 


Test  precipitate  for  Cr  as  on  page  58.  Add  HNO3  to  filtrate 
till  acid,  then  divide  into  two  parts;  test  one  for  P2O5  with 
(NH4)2Mo04. 

Test  the  other  for  Al  by  adding  NH4OH  till  alkaUne,  when 
precipitate  will  be  AIPO4,  insoluble  in  acetic  acid. 

To  the  solution  of  Mn  and  Zn  chlorides  add  a  little  HCl  and 
boil.  Then  make  alkaline  with  NH4OH,  add  (NH4)2S,  warm 
slightly  and  filter.  The  precipitate  (MnS  and  ZnS)  may  be 
dissolved  in  cold  dilute  HCl  and  tested  for  Mn  and  Zn  as  in 
analysis  of  Group  IV,  page  67. 

OUTLINE  SCHEME  FOR  ANALYSIS  OF  GROUPS  III,   IV,  AND  V. 

(Phosphates,  oxalates,  borates,  etc.,  being  present.) 
To  filtrate  from  Group  II  add  NH4CI  and  NH4OH.     Heat  and  add  (NH4)2S. 
Filter  rapidly. 


Precipitate  =  MnS,  ZnS,  CoS,  NiS,  FeS,  Al(OH)3,  Cr(OH)3,  also  phosphates,  etc., 
soluble  in  acids  only.  Fuse  part  of  precipitate  and  test  for  Mn  (page  63).  Treat 
remainder  c  cold  dilute  HCl. 


Residue  = 

CoS  and 
NiS.    Make 
borax-bead 

test  and 
separate  Co 

if  neces- 
sary, c 
KNO2 

(page  67) . 


Solution=Mn,  Zn,  Cr,  and  Al.     Divide  solution  into  three  parts  of 
about  1/8,  2/8,  and  s/8,  respectively,  and  treat  as  follows: 


Filtrate, 

members  of 

Ba  and  K 

groups 


I. 

Test 

small 

portion 

forFe 

(pagess). 


II. 
To  second  portion  add  di- 
lute H2SO4. 


Precipitate 
may  be 
BaS04, 
SrSOi  or 
CaSO,.     Fil- 
ter, wash, 
fuse  c 
Na2C03  and 
KjCOj.     Dis- 
solve  fusion 
in  HA  and 
analyze  for 
Group  V. 


Solution = 
GaS04. 

Add  alco- 
hol; if  pre- 
cipitate oc- 
curs, filter, 
dissolve  in 

H2O,  and 

test  with 

ammonium 

oxalate. 


III. 
To  third  portion  add  FeCU  to  combine 
c  H3PO4,  etc.,  then  add   NaaCOa  or 
K2CO3,  and  BaC03  (page  89). 


Precipitate  =  Cr,  Al,  Fe,  and 
BaCOs.  Boil  precipitate 
5  NaOH  and  filter. 


Residue  = 

Cr,  BaCOj, 

etc.     Test 

for  Cr  as  on 

page  59- 


Solution^ 

KAIO2. 

Test  for  Al 

as  on  page 

59- 


Solution  = 
Mnand  Zn. 
Reprecipi- 

tate  Mn 
and  Zn  as 
sulphides, 

■and  test 
according 
to  page  67. 


CHAPTER  DC. 

ANALYTICAL   REACTIONS    OF   THE   ACIDS. 

In  the  analytical  processes  thus  far  described  we  have  con- 
sidered only  the  separation  and  detection  of  the  basic  or  metalHc 
part  of  the  salt  (positive  ions),  that  is,  we  have  analyzed  a 
solution  of  ferric  chloride,  and  found  the  iron  only.  It  is  neces- 
sary to  find  the  chlorine  (negative  ion).  Before  making  any 
examination  for  negative  ions,  it  will  be  possible  to  save  a  con- 
siderable amount  of  both  time  and  labor  by  first  carefully  con- 
sidering what  acids  are  capable  of  forming  soluble  salts  with  the 
bases  which  have  already  been  detected.  To  facihtate  this 
consideration  a  table  of  solubiUties  will  be  found  below  and  on 
the  following  page,  by  a  careful  study  of  which  it  will  be  possible 
to  select  such  acids  as  are  most  Hkely  to  be  present  in  the  un- 
known solution  under  investigation,  and  also  to  neglect  a  num- 
ber of  acids  which,  from  the  solubility  of  their  salts,  together  with 
the  character  of  the  solution  (acid,  alkaHne,  neutral  and  aqueous, 
or  otherwise),  will  necessarily  be  absent. 


TABLE 

SHOWING 

THE   SOLUBILITY 

OF 

SALTS 

K 

Na 

NH4 

Mg 

Ba 

Sr 

Ca 

Mn 

Zn 

Co 

Ni 

Fe 

Fe2 

Acetate 

w 

w 

w 

w 

w 

w 

w 

w 

w 

w 

w 

w 

w 

Arsenate 

w 

w 

w 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

Arsenite 

w 

w 

w 

a 

wa 

wa 

a 

a 

a 

a 

a 

a 

Borate 

w 

w 

w 

wa 

a 

a 

a 

a 

a 

a 

a 

a 

a 

w 
w 

w 
w 

w 
w 

w 
a 

w 
a 

w 
a 

w 
a 

w 
a 

w 
a 

w 
a 

w 
a 

w 
a 

w 

Carbonate 

a 

Chlorate 

w 

w 

w 

w 

w 

w 

w 

w 

w 

w 

w 

w 

w 

Chloride 

w 

w 

w 

w 

w 

w 

w 

w 

w 

w 

w 

w 

w 

Chromate 

w 

w 

w 

w 

a 

wa 

wa 

w 

w 

a 

a 

w 

a 

a 

ai 

ai 

ai 

Iodide 

w 

w 

w 

w 

w 

w 

w 

w 

w 

w 

w 

w 

w 

Nitrate 

w 
w 

w 
w 

w 
w 

w 
a 

w 
""a 

w 
a 

w 
a 

w 
a 

w 

a 

w 
a 

w 
a 

w 
a 

w 

Oxalate 

a 

Oxide 

w 

w 

a 

w 

w 

w 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

Silicate 

w 

w 

a 

a 

a 

a 

a 

"    a 

a 

a 

a 

a 

w 

w 

w 

1 

i 

Wl 

w 

w 

w 

w 

w 

w 

w 

w 

w 

a 

a 

a 

a 

a 

a 

Sulphocyanate 

w 

w 

w 

w 

w 

w 

w 

w 

w 

w 

w 

w 

w 

w 

w 

w 

wa 

a 

a 

a 

wa 

a 

w 

a 

wa 

w 

91 


92      SALTS  OF   THE   METALS   AND  QUALITATIVE  ANALYSIS 


TABLE  SHOWING  THE  SOLUBILITY  OF  SALTS.  —  CONCL  UDED. 


Cd 


Acetate 

Arsenate 

Arsenite 

Borate 

Bromide 

Carbonate 

Chlorate 

Chloride 

Chromate 

Cyanide 

Iodide 

Nitrate 

Oxalate 

Oxide 

Phosphate 

Silicate 

Sulphate 

Sulphide 

Sulphocyanate 
Tartrate 


Cr2 

Alj 

Sb 

Sn" 

Sn" 

Au 

Ag 

Hg2 

Hg 

Pb 

Bi 

Cu 

w 

w 

w 

w 

w 

wa 

wa 

w 

w 

w 

w 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

w 

w 

wa 

w 

w 

w 

1 

ai 

wa 

Wl 

wa 

w 

a 

a 

a 

a 

a 

a 

w 

w 

w 

w 

w 

w 

W 

w 

w 

w  &  i 

w 

wa 

w 

w 

w 

1 

at 

w 

Wl 

wa 

w 

a 

a 

a 

a 

a 

wa 

ai 

a 

w 

a 

w 

1 

w 

a 

wa 

a 

w 

w 

wa 

w 

w 

a 

1 

a 

a 

wa 

a 

a 

w 

w 

a 

a 

w 

w 

w 

w 

a 

w 

w 

a 

a 

a 

w 

a 

a 

a 

a 

a 

a 

a&  i 

a&  1 

a 

a 

a  &  1 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

ai 

a 

a 

w&a 

w 

a 

w 

w 

wa 

wa 

wa 

1 

a 

w 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

w 

w 

1 

a 

w 

a 

a 

w 

w 

w 

wa 

a 

a 

a 

a 

a 

wa 

wa 
wa 


w,  soluble  in  water;  a,  insoluble  in  water,  soluble  in  acids;  i,  insoluble  in  water  or  acids;  wa, 
sparingly  soluble  in  water,  readily  soluble  in  acids;  wi,  sparingly  soluble  in  water  and  acids;  ai, 
sparingly  soluble  in  acids  only. 

In  this  connection  it  is  well  to  remember  that  practically  all 
nitrates  and  chlorates  are  soluble  in  water;  sulphates  are  mostly 
soluble,  except  those  of  barium,  strontium,  and  calcium.  Phos- 
phates (di-  or  trimetallic) ,  silicates,  oxalates,  and  borates  are 
practically  insoluble,  except  those  of  the  alkaline  metals.  This 
latter  statement  is  also  true  of  carbonates,  except  that  some  of 
the  carbonates  will  dissolve  to  an  appreciable  extent  in  water 
containing  carbon  dioxide.  Chlorides,  bromides,  and  iodides 
are  nearly  all  soluble  except  those  of  the  first-group  metals. 
Sulphides  are  insoluble  except  those  of  Groups  V  and  VI.  Acid 
salts  are  usually  more  soluble  than  neutral  salts. 

In  making  qualitative  tests  for  the  negative  ions  it  is  not 
necessary  to  separate  them  one  from  the  other,  as  it  is  in  the 
case  of  metals ;  hence  the  tests  are  individual  ones,  usually  made 
upon  the  original  substance  or  solution,  and  often  require  con- 
firmation before  conclusive  evidence  is  obtained.  The  grouping 
is,  therefore,  simply  for  convenience,  as  it  thus  becomes  possible 
to  exclude  a  considerable  number  of  acids  by  a  single  general  test. 


analytical  reactions  of  the  acids  93 

Acid  Groups  (negative  ions). 

Group  I  may  include  such  acids  as  give  effervescence  when 
their  dry  salts  are  treated  with  dilute  H2SO4,  as  H2CO3,  H2S, 
H2S2O3,  H0SO3  and  HCN. 

Group  II  may  include  acids  giving  a  precipitate  with  AgNOs 
in  dilute  HNO3  solution,  as  HCl,  HBr,  HI,  HCN,  HCNS,  HNO2, 
HCIO,  H4FeCy6,  H3FeCy6,  H2S2O3,  H2S  and  HPH2O2. 

This  second  group  may  be  further  subdivided  into  three  parts 
according  to  the  color  of  the  precipitate  obtained  (pages  95  and 

97)- 

Group  III  may  include  acids  forming  insoluble  salts  with 

BaCL  or  CaCl2  and  not  found  in  Groups  I  or  II,  as  H2SO4,  H2C2O4, 
H3PO4,  H3BO3,  H2Cr04  and  H2Si03. 

Group  IV:  We  may  put  in  Group  IV  any  acids  not  included 
in  the  foregoing  groups.  Of  common  occurrence  are  nitric 
(nitrates),  chloric  (chlorates),  and  acetic  (acetates). 

Detection  of  Acids  of  Group  I. 

(Acids  effervescing  with  dilute  sulphuric  acid.     H2CO3,  H2S,  H2SO3,  H2S2O3,  HCN.) 

To  a  test-tube  a  quarter  full  of  the  unknown  solution,  or  a 
little  dry  substance  on  a  watch-glass,  add  dilute  H2SO4.  If 
solution  is  very  dilute,  concentrate  it  before  making  test,  as  a 
slight  amount  of  gas  might  be  absorbed  by  the  water.  Watch 
carefully  for  any  escape  of  gas  and  note  any  odor  which  may  be 
given  off. 

Carbonates  evolve  CO2,  odorless,  but  if  passed  into  lime-water 
or  baryta-water  will  give  white  precipitate  of  CaCOs  or  BaCOs. 

Sulphides  evolve  H2S,  odor  of  rotten  eggs.  Confirm  by 
adding  a  little  dilute  H2SO4  to  the  suspected  powder  (or  solu- 
tion) in  a  test-tube  and  holding  over  the  mouth  of  the  tube  a 
piece  of  filter-paper  wet  with  a  solution  of  lead  acetate.  The 
test-tube  may  be  warmed  slightly  to  expel  the  gas,  when  a  dark- 


94      SALTS  OF  THE  METALS  AND  QUALITATIVE  ANALYSES 

colored  stain  will  appear  on  the  filter-paper,  due  to  the  formation 
ofPbS. 

Sulphites  evolve  SO2,  odor  of  burning  sulphur.  Sulphites 
ill  neutral  solution  may  be  further  identified  by  the  deep-red 
color  produced  with  ferric  chloride.  The  color  is  discharged 
upon  addition  of  dilute  acids,  HCl,  or  H2SO4  (difference  from 
HCNS). 

Thiosulphates  also  evolve  SO2,  but  at  the  same  time  the 
mixture  becomes  cloudy  from  precipitation  of  sulphur.* 

Thiosulphates  in  neutral  solution  treated  with  ferric  chloride 
give  a  violet  to  purple  color,  fading  (rapidly  upon  warming)  to 
a  colorless  solution.  In  mixtures  of  sulphites  and  thiosulphates 
both  acids  may  often  be  detected  by  the  use  of  FeCls,  the  deep- 
red  coloration  of  the  mixed  acids  rapidly  fading  to  the  fighter  red 
of  Fe2(S03)3  (not  to  colorless  solution). 

Cyanides  evolve  HCN,  odor  of  peach-stones.  (Mercuric 
cyanide  does  not  respond  to  this  reaction.)  Confirm  by  reactions 
given  under  Group  11. 

Preliminary  Tests  for  Common  Acids  of  Groups  11  and  in. 

(In  preparatory  courses  the  acids  given  in  this  list  may  be  sufficient.) 

From  the  acids  of  Group  II  and  III  it  may  be  desirable  to 
select  for  laboratory  practice,  at  least  at  the  beginning  of  the 
acid  work,  the  more  common  members  of  the  groups.  These 
will  be  HCl,  HBr,  HI,  HCN,  and  H2S  of  Group  II  and  H2SO4, 
H2C2O4,  and  H3PO4  of  Group  III;  and  tests  for  them  may  be 
made  as  follows: 

Chlorides  give  with  AgNOa  in  presence  of  HNO3  a  white 
curdy  precipitate  of  AgCl,  much  more  freely  soluble  in  ammonia 
than  any  other  acid  of  the  group  here  given  except  the  cyanide 

*  Sulphides  may  also  precipitate  sulphur  in  presence  of  compounds  capable  of 
oxidizing  the  H2S,  such  as  FeCls.  In  the  absence  of  sulphates  either  H2SO3  or 
H2S2O3  can  be  oxidized  to  H2SO4  by  heating  with  HNO3  and  a  precipitate  of  BaS04 
obtained  with  BaCU. 


ANALYTICAL  REACTIONS  OF   THE  ACIDS  '95 

AgCN,  but  HCN  is  a  member  of  the  first  acid  group  and  would 
have  been  pre\iously  detected. 

Bromides  with  AgNOs  and  HNO3  give  a  precipitate  of  AgBr 
similar  in  appearance  to  AgCl,  but  with  a  slightly  yellowish 
color  and  only  sparingly  soluble  in  NH4OH. 

The  tests,  described  on  page  97,  should  also  be  made  if 
bromides  or  iodides  are  suspected  in  the  solution. 

Cyanides,  see  Group  I. 

Sulphides  will  give  a  black  precipitate  with  AgNOs,  and 
have  been  pre^•iously  considered  in  Group  I.  _ 

Sulphates  may  be  detected  by  first  acidifying  the  solution 
strongly  ^\dth  HCl  (filtering  out  a  precipitate  if  any  occurs) 
and  adding  a  solution  of  BaClo",  a  white  precipitate  will  then  be 
BaS04,  showing  presence  of  sulphates  in  solution  tested. 

Phosphates  in  a  solution  containing  HNO3  and  free  or  nearly 
free  from  HCl  will  give,  with  ammonium  molybdate,  a  yellow 
cr}'stalline  precipitate  of  ammonium  phosphomolybdate. 

Oxalates  may  be  detected,  in  a  solution  free  from  sulphates 
and  which  is  slightly  acid  with  acetic  acid,  by  simple  addition 
of  calcium  chloride,  which  will  precipitate  CaC204,  white  and 
crystaUine. 

Detection  of  iVciDS  of  Group  II. 

(Giving  precipitate  with  AgNOa  in  presence  of  dilute  HNO3.) 

To  the  solution  to  be  tested  add  a  very  slight  amount  of 
HNO3  and  a  few  cubic  centimeters  of  x^gNOa  solution.  A  pre- 
cipitate indicates  acids  of  this  group. 

(a)  If  the  precipitate  is  white,  the  presence  of  chlorides  (HCl) , 
cyanides  (HCN),  sulphocyanates  (HCNS),  ferrocyanates 
(HiFeCye),  h}'pochlorites  (HCIO),*  or  nitrites  (HNO2)  is  in- 
dicated. 

*  Precipitate  is  AgCl.  Reaction  is  3  XaClO  +  3  AgNOs  =  2  AgCl  +  AgClQi 
+  3  NaNOs. 


96      SALTS  OF   THE  METALS  AND  QUALITATIVE   ANALYSIS 

To  separate  or  identify  these  silver  precipitates  allow  to 
settle,  decant  the  supernatant  fluid,  and  add  NH4OH.  Shake 
thoroughly,  when  the  chloride  (AgCl),  cyanide  (AgCN),  and 
nitrite  (AgN02)  will  dissolve  easily,  the  sulphocyanate  (AgCNS) 
and  the  ferrocyanide  (Ag4Fe(CN)6)  slowly  or  sKghtly. 

If  KCNS,  or  H4Fe(CN)6  is  indicated,  test  original  solution 
with  a  few  drops  of  FeCls.  Sulphocyanates  or  thiocyanates 
(HCNS)  give  a  deep  blood-red  solution.  The  color  is  soluble 
in  ether  and  may  be  discharged  by  HgCl2.  Ferrocyanides 
(H4Fe(CN)6)  give  a  deep-blue  precipitate.     (See  page  55.) 

Acids  forming  white  silver  precipitates,  easily  soluble  in 
ammonia,  may  be  distinguished  as  follows: 

Chlorides  (HCl)  may  be  distinguished  from  HBr  and  HI 
by  the  ready  solubility  of  the  silver  precipitate  in  NH4OH.  If 
bromides  and  iodides  are  present,  liberate  the  halogens  by  means 
of  MnOa  and  H2SO4  and  pass  the  mixed  gases  into  a  solution  of 
aniline  in  acetic  acid  (4  c.c.  of  saturated  aqueous  solution  of 
anihne  and  i  c.c.  glacial  acetic  acid).  Iodine  gives  no  precipi- 
tate, bromine  gives  a  white  one  and  chlorine  a  black  one.  (Pres- 
cott  and  Johnson,  page  336.) 

This  is  a  delicate  and  very  satisfactory  test  for  bromine  but 
not  so  delicate  for  chlorine  in  the  presence  of  bromides.  For 
such  cases  the  following  chloro-chromic  anhydride  test  is  recom- 
mended. Neutralize  the  solution  if  necessary,  evaporate  to 
dryness,  transfer  residue  to  a  test-tube  of  rather  small  diam- 
eter, add  a  little  soHd  K2Cr207,  then  concentrated  H2SO4.  De- 
cant the  fumes  into  a  wider  test-tube  containing  a  few  cubic 
centimeters  of  NH4OH. 

If  the  chloro-chromic  anliydride  is  evolved,  ammonium 
chromate  will  be  formed.  Test  by  making  acid  with  acetic 
acid,  then  adding  acetate  of  lead.  A  yellow  precipitate  of  lead 
chromate  indicates  chlorine  in  the  original  solution. 

Hypochlorites  liberate  I  from  KI  without   the  addition  of 
acid. 


ANALYTICAL   REACTIOXS   OF    THE   ACIDS  gj 

Nolc.  —  Hypochlorite  solutions  arc  usually  quite  strongly  alkaline,  and  in  such 
cases  a  considerable  amount  of  iodide  is  necessary  to  obtain  the  characteristic  color 
in  chloroform  or  with  starch. 

Nitrites  liberate  I  from  KI  after  the  addition  of  acetic  acid. 
They  also  give  a  brown  coloration  with  acetic  acid  and  a  crystal 
of  ferrous  sulphate.     (Nitrates  require  a  stronger  acid.) 

Nole.  —  This  test  is  much  more  delicate  than  either  of  the  others  given,  and 
if  the  solution  is  very  dilute  it  is  well  to  make  it,  even  if  the  indigo  color  is  not 
discharged. 

Further  mLx  a  little  of  the  solution  with  a  few  cubic  centi- 
meters of  dilute  indigo  solution  and  shake.  The  indigo  is  de- 
colorized by  either  hypochlorites  (HCIO)  or  by  nitrites  (HNO2). 

Cyanides  may  be  t,ested  for  as  under  Group  I.  If  this  test  is 
not  conclusive,  they  may  be  converted  into  sulphocyanides  by 
the  addition  of  a  few  drops  of  (NH4)2S  and  evaporation  on  the 
water-bath  to  dryness.  It  may  then  be  dissolved  in  a  little  dis- 
tilled H2O,  filtered  and  tested  with  FeCls. 

{b)  The  precipitate  is  red-brown  or  orange,  soluble  in 
NH4OH  =  HsFeCye.     Ferricyanide  indicated. 

(c)  The  precipitate  is  black  or  turns  black  upon  warming: 
HoS  turns  black  immediately.  HHoPOo  starts  to  precipitate 
white,  but  rapidly  turns  black,  H2S2O3  precipitates  white  and 
turns  black  slowly  or  upon  heating. 

Sulphides  (H2S)  and  thiosulphates  (H2S2O3)  may  also  be 
detected  as  described  under  Group  I,  Acids. 

{d)  If  the  precipitate,  originally  obtained,  is  yellow  and  in- 
soluble in  NH4OH,  iodides  are  indicated;  if  yellowish  white  and 
slowly  soluble  in  NH4OH,  bromides  are  probably  present. 

Iodides  and  bromides  (HI  and  HBr)  may  be  detected  in 
the  same  solution  by  adding  chlorine  water,  very  cautiously  at 
first,  and  shaking  with  chloroform.  The  chlorine  hberates  the 
iodine,  which  is  dissolved  by  the  chloroform  with  violet  color. 
Excess  of  chlorine  decolorizes  the  iodine  and  liberates  the  bromine 
which,  in  turn,  is  dissolved  by  the  chloroform  with  yellow  to 
red  color. 


98      SALTS   OF    THE   METALS  AXD  QUALITATIVE   AXALYSIS 

Acid  Group  III. 

( \cids  forming  insoluble  barium  or  calcium  sails,  nol  included  in  Ihe  Acid 
Group  I  or  II.) 

The  members  of  this  group  may  be  separated  from  each 
other,  although  this  is  not  necessary  unless  several  members 
are  present.  H2SO4,  H2C2O4,  H2Cr04,  H2Si03,  H3BO3,  H3PO4, 
separated  as  follows:  To  a  little  of  the  unknown  solution  add 
2  or  3  c.c.  of  HCl;  a  white  or  gelatinous  precipitate  which  is  not 
dissolved  by  dilution  with  water  and  warming  is  probably  silicic 
acid.  Make  a  bead  test  with  microcosmic  salt;  the  particles  of 
SiOo  remain  undisturbed  by  the  hot  bead,  forming  the  so-called 
silicon  "  skeleton."  Filter  out  the  silicic  acid  and  add  CaCl2 
or  a  mixture  of  BaCl2  and  CaCl2;  a  white  precipitate  wdll  be 
BaS04*  (test  for  sulphates),  the  Ba  and  Ca  salts  of  all  remain- 
ing acids  of  the  group  being  soluble  in  HCl. 

Filter  out  the  BaS04,  and  to  the  filtrate  add  NH4OH,  w^hich 
will  cause  a  precipitate  of  barium  oxalate,  chromate,  borate,  and 
phosphate.  Filter,  wash  precipitate  two  or  three  times,  reject 
wash-water,  then  transfer  to  test-tube  by  making  a  small  hole  in 
point  of  paper  and  forcibly  wasliing  through  with  the  least  pos- 
sible amount  of  water;  acidulate  strongly  with  acetic  acid,  which 
will  dissolve  the  phosphates  and  borates,  leaxang  undissolved 
the  oxalates  (BaC204,  white)  and  chromates  (BaCr04,  yellow). 


Oxalic  and  chromic  acids  as  barium  salts. 


Phosphoric  and  boric  acids. 


*  If  the  HCl  is  too  strong,  BaCU  may  be  precipitated  as  such,  but  the  pre- 
cipitate in  this  case  will  form  more  slowly  than  the  BaSOj;  it  will  have  a  crystal- 
line appearance  and  will  dissolve  upon  addition  of  water. 


ANALYTICAL  REACTIONS  OF   THE  ACIDS  99 

Dmde  the  filtrate  into  two  parts,  {a)  and  {b).  Test  one 
part,  (a),  for  H3r04  by  adding  to  it  an  excess  of  ammonium 
molybdate*  (in  HNO3),  when  a  yellow  precipitate  (forming 
sometimes  after  several  hours'  standing)  is  ammonium  phospho- 
molybdate  (test  for  phosphates)]  the  mixture  may  be  warmed 
to  hasten  precipitation;  the  degree  of  heat  should  not  exceed 
40°  C,  as  the  ammonium  molybdate  might  be  decomposed, 
giving  a  yellow  precipitate  similar  to  the  phosphomolybdate. 

Note.  —  If  As  is  present,  it  must  be  removed  by  HoS  before  testing  for  H3PO4. 

Test  the  other  part,  (6),  for  H3BO3  by  evaporating  to  dryness 
in  a  porcelain  dish;  then  moisten  with  strong  H2SO4,  cover  with 
a  little  alcohol,  and  ignite.  Boric  acid  will  give  to  the  flame 
(particularly  the  edge)  of  the  burning  alcohol  a  green  color  due 
to  formation  of  ethyl  borate.  This  color  is  more  easily  apparent 
if  the  dish  is  placed  in  a  darkened  corner. 

A  test  for  H3BO3  may  also  be  made  with  turmeric  paper, 
wliich  if  dipped  into  a  solution  of  boric  acid,  or  of  a  borate  mixed 
with  HCl  or  H2SO4  to  slight  but  distinct  acid  reaction,  and  dried 
at  100°,  becomes  red;  the  red  color  becomes  bluish  black  or 
greenish  black  when  moistened  with  a  solution  of  an  alkali  or 
an  alkaline  carbonate.  If  there  is  a  suspicion  that  H2Cr04  and 
H2C2O4  are  both  present,  dissolve  the  precipitate  of  barium 
oxalate  and  chromate  off  the  paper  with  dilute  HCl;  divide  the 
filtrate  into  two  parts  and  test  one  for  H2Cr04  by  addition  of 
H2O2,  which  \dth  chromates  in  presence  of  HCl  produces  a  deep- 
blue  solution  and  ultimately  CrCls. 

In  the  absence  of  chromates,  the  precipitate  being  white, 
oxalates  may  be  confirmed  by  coloring  the  second  part  of  the 
solution  a  faint  pink  with  a  dilute  solution  of  KMn04  and  warm- 
ing, when  the  color  will  be  discharged. 

In  the  presence  of  chromates,  the  precipitate  being  yellow, 
it  vnYL  be  necessary  to  test  the  original  solution  for  oxalates 

*  Preparation  of  ammonium  molybdate  solution,  appendix,  page  424. 


lOO     SALTS  OF   THE  METALS  AND  QUALITATIVE  ANALYSIS 

as  follows:  To  a  few  centimeters  of  the  unknown  add  alcohol; 
warm.  The  chromate  will  be  reduced  to  CrCls.  Add  NH4OH 
till  alkaline  and  filter  out  the  precipitate,  Cr(0H)3.  The  filtrate 
may  be  tested  for  oxalic  acid  as  above,  or  with  CaCl2,  a  white 
precipitate  being  CaC204. 

Acids  of  Group  IV. 

The  remaining  acids  of  importance  not  included  in  either 
of  the  three  preceding  groups  are  nitric,  HNO3,  chloric,  HCIO3, 
and  acetic,  HC2H3O2. 

Nitrates.  —  Saturate  5  c.c.  of  a  very  dilute  nitrate  solution 
with  FeS04.  Filter  and  carefully  underlay  the  clear  filtrate 
with  concentrated  sulphuric  acid;  a  dark  ring  (pale  red-brown 
to  nearly  black)  at  point  of  contact  of  the  two  liquids  shows 
presence  of  a  nitrate. 

Chlorates.  —  A  solution  free  from  chlorides  or  hypochlorites 
treated  with  Zn  and  dilute  H2SO4  will  give  a  test  for  HCl  if 
chlorates  were  originally  present,  the  chlorate  having  been  re- 
duced by  the  nascent  hydrogen : 
2  KCIO3  +  6  Zn  +  7  H2SO4  =  6  ZnS04  +  K2SO4  +  2  HCl  +  6H2O. 

Boiling  with  sulphurous  acid  also  reduces  HCIO3  (and  HCIO) 
to  HCl. 

If  the  substance  is  in  solid  form,  a  very  small  particle  may 
be  warmed  with  concentrated  H2SO4.  Chlorates  detonate  and 
give  off  yellow  fumes  of  CIO2 : 

3  KCIO3  +  2  H2SO4  =  2  KHSO4  +  KCIO4  +  2  CIO2  +  H2O. 

Acetates  give  with  ferric  chloride  a  red  color  which  is  not 
discharged  by  HgCl2  (difference  from  sulphocyanate),  but  may 
be  discharged  by  HCl  (difference  from  sulphocyanate  and 
meconate). 

A  more  positive  test  is  the  formation  of  the  ethyl  ester  or 
acetic  ether.  A  blank  test  for  comparison  should  always  be 
made,  the  method  of  procedure  being  as  follows: 


ANALYTICAL  REACTIONS  OF   THE  ACIDS  lOI 

Take  two  test-tubes  of  practically  equal  diameter,  mix  in 
each  equal  volumes  of  alcohol  and  strong  sulphuric  acid;  warm 
the  tubes  together;  then  into  one  introduce  a  few  centimeters 
of  the  unknown  solution,  and  into  the  other  an  equal  volume  of 
water.  Heat  again  to  a  boiling-point  and  compare  the  odors  from 
the  two  tubes.     The  acetate  is  easily  detected  if  present. 


CHAPTER  X. 
ANALYSIS   IN   THE   DRY   WAY. 

In  the  examination  of  solid  substances  much  may  be  learned 
by  a  few  simple  tests  directly  appHed  to  the  substance,  which 
has  been  reduced  (if  necessary)  to  the  form  of  a  powder. 

Some  of  these  are  usually  used  as  prehminary  to  the  solu- 
tion of  the  substance  and  regular  analysis  in  the  wet  way.  These 
tests  may  be  made  quickly,  and,  with  a  little  elaboration,  will 
often  give  all  the  information  required  regarding  an  unknown 
substance. 

The  practical  questions  of  actual  experience  are  usually 
simple  ones.  It  is  not  an  analysis  of  an  unknown  solution 
possibly  containing  all  the  metals  of  one  or  more  groups  that 
interests  an  active  practitioner,  but  a  specific  inquiry  as  to 
whether  or  not  this  or  that  preparation  contains  or  does  not 
contain  the  necessary  or  the  undesirable  ingredient,  whether 
the  thing  is  of  the  composition  or  of  the  strength  represented, 
and  a  few  minutes'  work  in  the  laboratory,  especially  if  aided 
by  the  microscopical  tests  given  in  a  subsequent  chapter,  will  fre- 
quently be  found  suflficient  to  answer  questions  of  this  character. 

The  tests  made  in  the  dry  way  are  not  as  delicate,  nor  are 
the  results  obtained  (especially  negative  ones)  as  conclusive,  as 
those  of  a  systematic  analysis  of  the  substance  in  solution,  and 
in  occasional  cases  it  may  be  necessary  to  resort  to  the  more 
tedious  process. 

Before  undertaking  the  analysis  of  a  substance,  note  care- 
fully its  physical  properties  of  odor,  color,  and  solubility;  also 
whether  it  is  magnetic,  metaUic,  or  crystaUine. 


ANALYSIS  IN   THE  DRY   WAY  103 

The  volatile  acids,  certain  ammonium  compounds,  bromine, 
and  iodine  may  be  detected  frequently  by  their  odor. 

Colors  of  Salts  and  Solutions. 
The  following  colored  salts  are  soluble  in  water: 

Black Silver  albuminate  (argyrol,  etc.). 

Violet  or  purple Chromic  salts  and  permanganates. 

,  j  CrOa  and  acid  chromates,  KsF'eCye,  sodium- 

I       nitro-prusside,  HaPtCle. 

Reddish  brown  or  purple-red Manganic  salts. 

Reddish  yellow Ferric  salts  and  AuCls. 

,,  „  (  Neutral    chromates  of   the   alkalis,    salts  of 

Yellow \ 

[      uranmm. 

Pale  yellow KiFeCy^  (Potassium  ferrocyanide). 

pink Salts  of  cobalt. 

Pale  pink Manganous  salts. 

p  j  Ferrous    salts,    nickel    salts,    certain   copper 

I       salts. 

Dark  green Some  chromic  salts. 

Blue-green , Chromates. 

Blue Cupric  salts. 


The  following  colored  substances  are  insoluble  in  water: 


f  Carbon  and  carbides,  metals,  many  metallic 


Black \       sulphides,  oxides  of  Cu,  Fe,  Mn,  and  Pb. 

[       Iodine  is  bluish  black. 

Red HgO,  HgS,  Hgia,  PbjOi,  AS2S2. 

Brick-red Amorphous  phosphorus,  Fe203. 

Light  brown PbO  (litharge). 

f  S,    HgO,  CdS,  AS2S3,    Pbl2,  kgzVOi,   ammo- 
Yellow  \       nium    phosphomolybdate,    and    chromates 

I       of  the  heavy  metals,  PbCr04,  BaCr04. 
p  '  j  Some  copper  compounds,  CU2I2,  Paris  green, 

"^^^^ i       e"tc,,Cr203. 

_.  J  Some    copper    compounds,     Prussian    blue, 

ultramarine;  anhydrous  salts  of  cobalt. 


{ 


I04     SALTS  OF  THE  METALS  AND  QUALITATIVE  ANALYSIS 

METHODS  OF  EXAMINATION. 

Powder  the  substance  and  apply   tests  described  in   this 
chapter,  which  will  be  considered  in  the  following  order: 

A.  Ignition  with  free  access  of  air. 

B.  Closed- tube  test. 

C.  Flame  test  on  platinum  wire. 

D.  Examination  with  the  blow-pipe  on  plaster  slab. 

E.  Bead  tests  on  platinum  wire. 

F.  Special  tests,  distinguishing  or  confirmatory. 


A.    Ignition  in  Air. 

This  test  may  be  made  on  a  crucible  cover  or  on  platinum 
foil.  If  there  is  any  probability  of  I,  Br,  CI,  P,  or  easily  reduced 
metallic  compounds  in  the  unknown  substance,  the  platinum 
foil  is  likely  to  be  destroyed;  hence,  the  porcelain  is  recommended. 

The  heat  employed  should  be  very  low  at  first;  then  it 
should  be  gradually  increased  and  the  test  carefully  watched. 

The  majority  of  phenomena  occurring  under  A  are  more 
easily  observed  in  the  test  made  vdth.  closed  tube,  B,  and  will 
be  given  under  that  head. 


Observed  Phenomena. 
The  substance  melts  and  steam  is  given  off. 


The  substance  burns  (a)  at  comparatively  low 
temperature  with  blue  flame  and  odor  of 
SO2  or  burning  matches. 

(b)  With  yellow  flame  and  much  smoke. 

(c)  Blackens    and    then    burns   at    fairly    high 

temperature,   leaving  white  or  gray  ash. 

(d)  Blackens  without  burning. 

Vapors  are  given  off: 

(a)  Of  a  violet  color. 

(b)  Of  a  red-brown  color. 

(c)  Of  a  greenish-yellow  color. 

(d)  White,  practically  odorless. 


Indications. 

Water  of  crystallization. 
NH4NO3  or  H2C2O4,  which 
entirely  disappears. 

Sulphur. 


Fat,  waxes,  resins,  etc. 
Carbonaceous  matter  other 

than  fats,  etc. 
Formation  of  oxides  of  Fe, 

Co,  Ni,  or  Cu. 

Iodine. 

Br  or  nitrogen  oxides. 
Chlorine  or  CIO2. 
Some      ammonium      salts, 
NH4CI,    (NH4)2S04,    etc. 


ANALYSIS  IN   THE  DRY   WAY 


105 


Observed  Phenomena. 

(e)   White  with  odor  of  NH3. 
(/)   White  with  odor  of  garlic. 
{g)   White    and    j'cllow    with    ammoniacal    or 
empyreumatic  odor. 
The  substance  decrepitates. 

Examine  residue  on  foil  (porcelain);   add  a  drop 
or  two  of  water  and  test  with  litmus-paper. 
If  found  to  be  acid. 
If  alkaline  without  blackening. 

If  alkaline  with  blackening. 


Add  a  drop  of  dilute  HCl,  effervescence. 


Indications 

Ammonium  carbonate. 

Arsenic. 

Organic  matter. 

Water  held  mechanically  by 
crystals,  as  NaCl,  etc. 


Acid  salts. 

Fixed  alkali  hydrates  or 
carbonates. 

Carbonate  formed  by  com- 
bustion of  organic  com- 
pounds. 

Carbonates. 


B.    Closed-tube  Test. 

Select  a  tube  of  soft  glass  about  five  or  six  inches  in  length. 
Seal  one  end  and  enlarge  slightly.  Into  the  bulb  thus  formed 
introduce  a  few  grains  of  the  unknown  powdered  substance. 
Heat  carefully,  making  the  following  tests  at  various  stages  of 
the  process.     Note  the  odor  of  escaping  gases. 

Test  for  oxygen  by  inserting  a  glowing  splinter  into  the  tube. 

Test  for  combustible  gases  by  occasionally  applying  flame 
to  the  open  end  of  the  tube. 

Bring  to  the  mouth  of  the  tube  a  clear  drop  of  Ba(0H)2 
solution.     If  the  drop  becomes  turbid,  CO2  is  indicated. 


Observed  Phenomena. 

Steam  condenses  in  cold  part  of  tube. 
Oxygen  is  evolved. 


Carbon  Dioxide  is  evolved. 


A  Combustible  Gas  is  formed: 

(fl)    Burning    with    a    luminous   flame,    black 
residue  remains  in  tube. 

(b)  Burning  with  a  blue  flame. 

(c)  Burning  as  in  (b)  and  with  odor  of  SO2. 

A  Sublimate  forms  in  the  cooler  part  of  the 
tube.     Examine  under  microscope. 


Indications. 

See  under  A. 

A  peroxide,  chlorate,  some 
oxides  (as  HgO),  alkali 
nitrates. 

Carbonates,  oxalates  (at 
high  temperature),  or- 
ganic matter. 

Hydrocarbons  from  organic 

matter. 
CO  from  oxalates. 
H2S  from  moist  sulphides. 


Io6      SALTS  OF   THE  METALS  AND  QUALITATIVE  ANALYSIS 


Observed  Phenomena. 

Colorless  with  partial  decomposition. 

Color  is  u'liite   with   production   of   garlic  odor, 

crystalline. 
Color   is   'ii'hite   when   cold.     Yellow    when   hot, 

crystalline. 
Color    is    white  —  it    sublimes    directly    without 

melting  and  blackens  with  NH4OH. 
A    white    sublimate    which    by    treatment    with 

slaked  lime  yields  NH3. 
A  white  sublimate  of  A&2O3  with  black  residue 

in  tube  and  odor  of  acetic  acid. 
Sublimate    is    graj',    consisting    of    small    glob- 
ules which  can  be  made  to  unite  by  rubbing. 
Sublimate    consists    of    reddish    yellow    to    red 

globules,  yellow  when  cold. 
Sublimate  darker  than  above  and  reddish  yellow 

when  cold. 
Sublimate  is  brown  to  black  "metallic  mirror," 

soluble  in  NaClO. 
Ditto;   dead  black,  insoluble  in  NaClO. 
Sublimate  is  black  accompanied  by  violet  vapor. 

Sublimate    black,    turning    red    when    rubbed. 
No  sublimate  is  formed,  but  the  color  changes 
to 

Yellow  when  hot,  white  when  cold. 

Reddish  brown  when  hot,  yellow  when  cold. 

Black  when  hot,  red  when  cold. 

Black  when  hot,  brick-red  when  cold 

Dark  orange  when  hot,  yellow  when  cold. 
Black    residue    without    other    visible    mani- 
festation. 
Substance    melts    without   a    sublimate    being 
formed. 


Indications. 

0.xalic  acid.  Plate  I,  Fig.  i. 
AS2O3.     Plate  I,  Fig.  2. 

HgCU.     Plate  I,  Fig.  3. 

HgCl. 

Ammonium  salts.     Plate  I, 

Fig.  4. 
Paris  green. 

Hg    from    HgO,   amalgam, 

etc.     Plate  I,  Fig.  5. 
Sulphur. 

Native  sulphide  of  arsenic. 

IMctallic  arsenic. 

Metallic  antimony. 
Iodine.     Plate  I,  Fig.  6. 
HgS,  cinnabar. 


ZnO. 

PbO  or  BiaOs.     (See  D.) 

HgO  (Hg  sublimes). 

FC2O3. 

Chromates  of  Pb,  etc. 

O.xides  of  Cu,  Co,  etc.     (See 

A.) 
Salts  of  the  alkaline  metals. 


C.   Flame  Test  \vith  Platinum  Wire. 

Introduce  the  substance  on  platinum  wire  into  the  edge  of 
the  flame.  More  satisfactory  results  are  sometimes  obtained 
if  the  soHd  is  first  moistened  with  HCl  (page  80,  note).  The 
flame  is  colored  as  follows:  by  Na,  yellow;  K,  violet;  Ni,  car- 
mine; Sr,  crimson;  Ca,  orange-red;  Ba,  yellowish  green;  Cu, 
usually  bright  green;  CUCI2,  an  intense  blue;  H3BO3,  pale  green; 
Sb,  greenish  blue;  Pb,  As,  Bi,  hvid  blue. 


PLATE  I.  —  SUBLIMATES. 


Fig.  I. 
Oxalic  Add  (Sublimed). 


Fig.  3. 
^Mercuric  Chloride  (Sublimed). 


Fig.  2. 
Arsenic  Trioxide. 


Fig.  4. 
Ammonium  Sulphate  (Sublimed)". 


Fig.  5. 
^Mercury  from  H2O. 


Fig.  6. 
Iodine. 


ANALYSIS  IN   THE  DRY   WAY  107 

D.    Blowpipe  Test  on  Plaster.* 

Smooth  plaster  slabs  about  one  inch  wide  and  four  inches 
long  are  well  suited  for  these  tests.  These  may  be  prepared  by 
making  a  magma  of  calcined  plaster  and  pouring  upon  a  glass 
plate.  Before  it  hardens  mark  deeply  with  a  spatula  into  slabs 
of  desired  shape  and,  after  it  is  thoroughly  dried,  break  as  marked. 

Make  a  little  depression  near  one  end  of  the  slab  and  in  it 
place  a  small  amount  of  the  substance  to  be  tested;  then  if 
a  fine  oxidizing  flame  is  made  to  play  over  the  surface  of  the 
assay,  characteristic  coatings  of  oxide  or  sublimate  may  be 
obtained. 

In  many  cases  the  character  of  the  substance  may  be  deter- 
mined more  easily  by  first  moistening  the  assay  with  various 
reagents.  Tetrachloride  of  tin,  cobalt  nitrate,  and  "  sulphur 
iodide  "  are  the  most  valuable  of  the  reagents  so  used.  The 
"  sulphur  iodide  "  is  not  of  definite  composition,  but  a  mixture 
of  about  equal  weights  of  sulphur  and  potassium  iodide. 

D.  I.     Examination  without  Reagents. 
Observed  Phenomena. 

Substance    melts    to    bright    metallic    globules 

with  brownish-yellow  deposit  near  assay. 
Requires  high  heat.     Assay  revolves. 
Substance   melts    to   bright   globule   with    coat- 
ing on   plaster,   deep  orange   when  hot,   light 

yellow  when  cold. 
Substance    remains    or    becomes    black    without 

melting.     No  coating  on  plaster. 
Substance  volatilizes  with  white  fumes,  but  leaves 

dark  stain;   gray  to  black. 
Substance   melts   with   white   or   gray   oxide   on 

assay. 
Forms   a    white   or   gray   oxide   without   fusion. 

Coating   on   plaster   is   yellow   over "- brownish 

black. 


Indications. 

Silver. 


Lead  or  bismuth.     (See  D. 
II.) 

Copper   or   iron.     (See   A; 

also  F.) 
Antimony  or  arsenic.     (See 

F.) 
Tin.     (See  D.  III.) 

Cadmium. 


*  Substances  sufficiently  identified  by  previous  tests  have  been  omitted.    This 
method  will  be  found  useful  mainly  in  the  identification  of  metals. 

The  author  was  greatly  aided  in  the  preparation  of  this  list  by  Mr.  Geo.  F.  S, 
Pearce  of  the  Harvard  Dental  School,  who  carefully  verified  each  test. 


Io8      SALTS  OF   THE  METALS  AND  QUALITATIVE  ANALYSIS 


Observed  Phenomena. 

Forms  bulky   white  oxide  with  active  combus- 
tion of  assay. 
Forms  gray  coating  easily  volatilized. 

Cherry-red  —  crimson  to  black  according  to 
amount  of  substance  deposited.  Odor  of 
rotten   horse-radish;     coating   not   permanent. 

White  coating  or  white  fumes  at  very  high  heat. 
Assay  burns  with  bluish-white  light. 

Silver-white.     Assay  remains  unchanged. 


Indications. 
Magnesium. 

Mercury   from    amalgams. 

(See  D.  II.) 
Selenium. 

Zinc.     (See  D.  III.) 
Platinum,  metallic. 


D.    II.    Cover  Substance  with  KI  and  S.     Use  Oxidizing  Flame. 


Obser\'ed  Phenomena. 

Dirty-white  and  light-gray  coating.  Treated 
with  fumes  of  strong  NH3  and  again  placed 
in  oxidizing  flame  gives  bright-red  color. 
Metallic  globule  is  dull  and  brittle. 

Dirty  white  half  an  inch  from  assay.  Brown 
directly  under  assay.  No  change  when  treated 
as  above  with  strong  ammonia  fumes.  Metallic 
globule  is  bright  and  malleable. 

No  coating  near  assay.  Lead-colored,  one  to 
one  and  a  half  inches,  shading  to  yellow. 

Coating  bright  red  when  hot,  fading  to  yellow 
when  cold. 

Fine  brown  coating,  very  volatile. 


Intdications. 


Bismuth. 

Lead. 

IMercury. 

Cadmium. 

Antimony. 


D.  III.     Examination  with  Solution  of  Cobalt  Nitrate. 

Heat  substance  on  plaster  in  the  oxidizing  flame,  moisten 
weU  with  cobalt  nitrate,  and  again  apply  oxidizing  flame. 

Obser\^d  Phenomena. 

Color  is  deep  blue. 

Substance  is  infusible. 

Color  is  fine  blue.     Substance  fusible. 

Color  is  yellowish  green. 
Drab  to  bluish  green. 


Indications. 

Aluminium. 

Infusible  silicates.  (See  F.) 

Alkaline  silicate,  borate,  or 

phosphate. 
Zinc. 
Tin. 


D.    IV.     Examination  with  Tetrachloride  of  Tin. 
Observed  Phenomena.  Indications. 


Coating  pale  blue  to  lavender. 
Coating  fine  blue,  in  places  almost  black. 
Delicate  pink  to  red  produced  only  by  oxidizing 
flame. 


Bismuth. 

Antimony. 

Neutral  and  acid  chromates. 


ANALYSIS  IN   THE  DRY   WAY  109 

E.    Bead  Tests. 

The  bead  tests  are  made  \\dth  borax,  as  described  on  page  61, 
or  in  a  similar  manner  with  microcosmic  salt,  NaNH4HP04, 
which  by  action  of  the  heat  gives  up  NH3  and  H2O,  becoming 
sodium  metaphosphate,  NaPOs.  These  substances  fused  on  a 
loop  of  platinum  wire  unite  with  many  of  the  metallic  oxides, 
forming  "  beads  "  of  various  characteristic  colors,  some  of  the 
more  important  being  given  below. 

With  Borax. 

Co  in  the  oxidizing  flame  gives  an  intense  blue  bead. 

Ni  gives  a  red-brown,  yellow  when  cold. 

Cu  gives  a  green,  blue,  or  bluish  green  when  cold. 

Cr  gives  green. 

Fe  gives  a  red,  yellowish  when  cold. 

Mn  gives  an  amethyst. 

With  Microcosmic  Salt. 

Cobalt,  copper,  nickel,  and  iron  give  colors  similar  to  those 
obtained  vdth  borax.  Manganese  gives  a  \'iolet  bead  when 
heated  in  the  oxidizing  flame,  but  a  colorless  one  in  the  reducing 
flame. 

F.    Special  Tests  Distinctive  or  Coneirmatory 

The  oxides  of  copper  and  iron  may  be  distinguished  by  adding 
a  drop  of  HNO3,  warming  gently  to  drive  off  excess  of  acid 
(high  heat  will  decompose  the  nitrate,  giving  the  oxide  again), 
and  then  adding  a  drop  of  solution  of  K-iFeCye-  Fe  will  give 
a  dark-blue  coloration;   Cu  will  give  a  brown. 

To  distinguish  between  As  and  Sb  stains,  add  a  drop  of  hy- 
pochlorite solution  (NaClO).  The  arsenic  stain  will  dissolve; 
the  antimony  stain  will  remain  unaffected  (see  page  36). 


no      SALTS  OF   THE   METALS  AND  QUALITATIVE  ANALYSIS 

Antimony  gives  a  very  characteristic  coating  on  plaster  if 
treated  with  tetrachloride  of  tin.  The  coating  is  bluish  black 
near  assay,  fading  away  to  a  very  delicate  color  at  greater 
distance.     It  appears  almost  immediately  and  is  permanent. 

In  case  of  suspected  silicates  make  the  "  silica  skeleton  "  with 
a  bead  of  microcosmic  salt  (page  98). 


PART    II. 
DENTAL  METALLURGY. 

INCLUDING  THE  CHEMISTRY  OF  ALLOYS,  AMALGAMS, 
SOLDERS,   AND    CEMENTS. 

CHAPTER  XL 
THE   METALS. 

Properties  of  the  Metals. 

Metals  are  malleable  in  order  as  follows  from  gold,  the  most 
malleable,  to  nickel,  the  least:  Au,  Ag,  Al,  Cu,  Sn,  Pt,  Pb,  Cd, 
Zn,  Fe,  Ni. 

Metals  are  tough  or  tenacious  in  order  as  follows:  Fe,  Cu, 
Pt,  Ag,  Au,  Al,  Zn,  Pb. 

The  ductihty  of  metals  ranges  from  greatest  to  least  as 
foUows:   Au,  Ag,  Pt, 'Fe,  Ni,  Cu,  Cd,  Al,  Zn,  Sn,  Pb. 

Metals  conduct  heat  and  electricity  in  the  same  order  until 
tin  is  reached.  From  tin  the  order  given  is  correct  for  iieat 
but  not  for  electricity:  Ag,  Cu,  Au,  Al,  Zn,  Cd,  Sn,  Fe,  Pb, 
Pt,  Bi. 

The  melting-point  of  the  various  metals  is  of  considerable 
importance  in  the  preparation  of  alloys.  The  following  table 
has  been  compiled  from  the  latest  available  results.  The  de- 
grees given  are  according  to  the  centigrade  scale : 

Ir 22C50°  Al 657° 

Pt 1780°-  Mg 500°  (burns) 

Ni 1450°     -  Sb 632° 

Cast  steel 1300°  Zn 41^°  (bums) 

Castiron... 1200°  Pb 327° 

Cu 1084°  Cd 322° 

Au 1075°  Bi 268° 

Ag 962°  Sn 232° 


112  DENTAL   METALLURGY 

If  lead,  which  is  the  softest  of  the  common  metals  is  taken 
as  a  standard  and  considered  as  one,  the  other  common  metals 
are  harder  in  the  proportion  shown  in  the  following  table  taken 
from  Hall's  Dental  Chemistry. 

Pb i.o      ■       Sb 1.8 

Sn 1.2  Zn 1.9 

Cd 1.4  Pt 2.0 

Al i-S  Cu 2.4 

Bi 1.6  Fe 2.4 

All 1.7  Ni 2.5 

Ag 1.8 

The  expansion  of  the  various  metals  under  the  influence  of 
heat  is  fairly  constant  and  there  have  been  determined  co- 
efficients of  expansion.  These  represent  the  amount  of  linear 
expansion  of  the  metals  due  to  a  rise  in  temperature  of  1°  C, 
usually  from  0°  to  1°.  The  coefficients  are  not  absolutely  con- 
stant, and  the  amount  of  expansion  observed  between  0°  and  1° 
may  differ  somewhat  from  that  between  50°  and  51°.  The 
coefficients  vary  widely  for  the  different  metals;  for  instance, 
in  passing  from  0°  to  100°  mercury  expands  1/16  of  its  Hnear 
measure,  copper  1/598,  and  platinum  1/1123. 

Hall's  Dental  Chemistry  gives  the  following  table  of  expan- 
sion from  cadmium  to  platinum  (0°  —  100°) : 

Cd 1/326  Ag 1/518  Ni 1/787 

Pb 1/342  Cu 1/598  Fe  (cast) 1/934 

Zn 1/343  Bi 1/617  Sb 1/952 

Al 1/432  Au 1/689  Pt 1/1123 

Sn 1/448 

According  to  the  kinetic-molecular  theory  every  metal  has 
a  certain  tendency  to  pass  into  solution  when  immersed  in  a 
fluid.  If  the  fluid  contains  the  ions  of  some  other  metal  of  less 
relative  electromotive  force  the  ions  in  solution  will  deposit 
upon  the  metal,  while  the  metal-ion  passes  into  solution;  i.e., 
the  one  metal  is  precipitated  by  the  other.  In  the  Hst  Au,  Pt,  Ag, 
Hg,  Bi,  Cu  (Pb,  Sn),  Co,  Cd,  each  metal  precipitates  all  pre- 


THE   METALS 


I-13 


ceding  it  (lead  and  tin  are  too  nearly  alike  for  either  to  com- 
pletely precipitate  the  other)  and  is  precipitated  by  all  which 
follow.  All  in  the  list  are  precipitated  by  Zn,  Mg,  Al,  K,  and  Na. 
Iron  precipitates  copper  and  the  preceding  metals  but  it  is 
only  partly  precipitated  by  those  which  follow. 

'  The  metals  are  electropositive  in  the  following  order  from 
zinc,  the  most  positive,  to  gold,  the  least:  Zn,  Cd,  Fe,  Ni,  Sn, 
Pb,  Cu,  Bi,  Sb,  Hg,  Ag,  Pt,  Au;  and  carbon  is  negative  to  all. 
It  will  be  noticed  that  tliis  Hst  of  metals  is  the  same,  but  in 
reversed  order,  and  is  arranged  for  the  same  reason  as  the  list 
given  in  the  paragraph  above. 

Thus  if  a  battery  is  constructed  with  zinc  as  represented  in 
the  cut  (Fig.  7),  and  iron  in  place  of  the  carbon,  then  the  iron  will 
be  electronegative  to  the  zinc,  and  hydrogen  will  be  evolved 
from  its  surface;   if,  on  the  other  hand,  iron  is  ,__^ 

used,  in  place  of  the  zinc,  and  the  carbon  remains  Zn 
as  in  the  cut,  the  iron  will  be  electropositive  to 
the  carbon,  and  oxygen  will  be  evolved  from  its 
surface.  This  property  of  metals  has  a  direct 
bearing  upon  dental  science,  because  human  saliva 
may  be  an  exciting  fluid  for  the  generation  of  gal- 
vanic currents,  its  activity  being  increased  by  an 
abnormal  reaction  either  acid  or  strongly  alkaline, 
and  it  is  only  necessary  to  place  in  the  mouth 
properly  related  metals,  as  amalgam  fillings  or  otherwise,  to  pro- 
duce the  elements  of  a  galvanic  battery. 

The  currents  thus  generated  are,  of  course,  infinitesimal,  but 
they  are  constant  and  may  aid  in  the  disintegration  of  fillings 
and  in  the  solution  of  the  constituent  metals.  Regarding  the 
extent  to  which  electric  currents  may  exist  in  the  mouth,  see 
Miller's  Micro-organisms  of  the  Human  Mouth. 


Fig.  7. 


CHAPTER  XII. 
ALLOYS. 

An  intimate  union  of  two  or  more  metals,  usually  produced 
by  fusion,  forms  an  alloy.  Such  a  union  of  one  or  more  metals 
with  mercury  is  an  amalgam. 

An  alloy  designed  to  be  used  in  the  preparation  of  dental 
amalgams  is  known  as  an  amalgam  alloy. 

Some  metals  can  be  fused  together  in  all  proportions,  as 
lead  and  silver.  Others  can  be  made  to  unite  only  in  Hmited 
proportions,  as  lead  and  zinc.  Lead  will  carry  only  i.6%  of  zinc, 
while  zinc  will  unite  with  only  1.2%  of  lead.  Excess  in  either 
case  separates  out. 

The  properties  of  an  alloy  are,  as  a  rule,  the  modified  proper- 
ties of  its  constituent  metals.  An  exception  to  this  rule  might 
be  made  of  the  sonorous  quality  of  bell-metal  and  like  alloys, 
this  being  hardly  a  property  of  the  constituent  metals  at  all. 

Following  are  some  of  the  more  common  alloys.  The  pro- 
portions given  are  general  formulae  and  may,  as  a  rule,  be  varied 
considerably: 

Aich's  metal,*  Cu  60%,  Zn  38.2%,  Fe  1.8%. 

Aluminium  bronze,  yellow,  resembles  gold,  Cu  92,  Al  8. 

Bell-metal,  Cu  80,  Sn  20. 

Brass,  Zn  i  part,  Cu  2  parts. 

Britannia  metal,  Cu  2,  Sn  82,  Sb  16. 

Bronze,  Cu  65  to  84,  Zn  from  31.5  to  11,  Sn  from  2.5  to  4. 

Coin  silver,  Ag  90,  Cu  10. 

Dental  alloys,  see  page  125. 

Dental  gold,  Cu  85,  Zn  15. 

*  Hepburn. 
114 


ALLOYS  ri5 

Dutch  metal,  Cu  84.5%,  Zn  15.5%. 

German  silver,*  Cu  50,  Ni  30,  Zn  20. 

Gun  metal,  Sn  11,  Cu  100. 

Mannheim  gold,  Cu  75%,  Zn  25%. 

Mosaic  gold,  Cu  50%,  Zn  50%. 

Solder,  sec  page  129. 

Sterling  silver  must  contain  92.5%  Ag. 

Type  metal,  Pb  78,  Sb  15,  Bi  7. 

For  fusible  metals  (Mellot's,  Wood's,  Rose's,  etc.)  see  page  1 28. 

Ail  alloys  (excluding  amalgams)  are  solid  at  ordinary  tem- 
peratures with  one  exception;  this  one  is  an  alloy  of  one  part 
potassium  with  three  parts  sodium. 

The  melting-point  of  an  alloy  is  often  lower  than  that  of  the 
metals  entering  into  its  composition  and  usually  lower  than  the 
mean  melting-point  of  its  constituents. 

In  making  alloys  the  tendency  to  separation  of  the  several 
metals  is  greater  if  the  alloy  is  allowed  to  cool  slowly;  hence 
three  essentials  in  the  process  are:  Complete  fusion,  which 
makes  possible  thorough  mixing,  and  after  this  has  been  attained 
rapid  cooling.  As  the  fused  mass  is  to  be  cooled  as  quickly 
as  possible  after  fusion  is  complete,  it  is  desirable  to  use  the  least 
amount  of  heat  practicable  in  effecting  the  desired  result..  To 
this  end  fuse  first  the  metal  with  the  lowest  melting-point, 
then  add  other  metals  in  the  order  of  their  melting-points. 
The  more  difficultly  fusible  metal  will  in  a  sense  dissolve  in 
the  more  easily  fusible  metal;  an  alloy  is  formed  and  its  tem- 
perature has  been  kept  far  below  the  melting-point  of  the  high 
fusing  constituent.  This  general  rule,  however,  may  be  modified 
by  the  proportion,  of  metal  used;  thus,  in  making  a  silver- tin 
amalgam-alloy  containing  60%. of  silver  it  is  better  first  to  melt 
the  silver  under  a  flux  of  carbonate  of  sodium  or  borax  to  prevent 
superficial  oxidation,   then  add  the  tin,  and  lastly  any  other 

*  Composition  of  different  samples  of  German  silver  may  differ  widely;  some 
contain  about  2.5%  of  iron  and  the  amount  of  copper  may  vary  from  40  to  60%. 


Il6  DENTAL   METALLURGY 

metal  to  be  used.  The  mixing  is  attained  by  stirring  with  a 
wooden  stick  and  the  cooling  by  turning  quickly  into  a  cold  clean 
mold.  For  class  work  or  in  making  small  amounts  (twenty 
grams)  of  alloy,  the  Fletcher  melting  arrangement  shown  in 
Fig.  8  is  very  convenient.  The  metals  are  melted 
in  the  graphite  crucible  and  then  by  tipping  up  the 
whole  contrivance  the  melted  metals  flow  back  into 
the  ingot  mold.  If  the  alloy  is  to  be  used  in  the 
preparation  of  dental  amalgams  it  must  be  re- 
duced to  fine  turnings  or  filings  suitable  for  ready 
amalgamation.  This  is  best  accomplished  in  the 
laboratory  by  means  of  a  coarse  file,  the  ingot  being  held  by  a 
vise.  The  fine  particles  of  iron  must  next  be  carefully  removed 
with  a  magnet,  and  then  the  filings  may  be  annealed  if  desired. 
The  annealing  of  the  amalgam-alloys  may  be  accomplished 
by  placing  the  freshly  cut  sample  in  a  dry  test-tube  and  keeping 
the  test-tube  in  boiling  water  for  ten  or  twelve  minutes.  It  has 
been  claimed  that  this  process  is  one  of  superficial  oxidation  and 
the  changes  produced  seem  to  be  consistent  with  this  theory. 
Again,  it  is  claimed  that  the  change  is  a  molecular  one  of  some 
sort  due  to  change  of  temperature,  and  Prof.  G.  V.  Black  has 
shown  that  an  alloy  will  anneal  as  rapidly  in  an  atmosphere  of 
nitrogen  as  of  oxygen.  The  modification  of  properties  produced 
by  annealing  varies  somewhat  with  the  composition  of  the  alloy; 
for  instance,  the  liability  to  discoloration  is  less  in  the  annealed 
than  in  the  unannealed  sample,  if  the  alloy  contains  silver  and  tin, 
or  silver,  tin,  and  zinc,  but  if  copper  is  a  constituent  the  reverse 
condition  has  been  found  to  exist. 

It  has  been  shown  that  the  freshly  cut  amalgam  alloys 
require  more  mercury  for  amalgamation  than  the  annealed 
alloy.  The  annealed  alloy  also  is  slower  in  setting  and  contains 
a  smaller  proportion  of  impurities  (metallic  oxides)  which  de- 
tract from  the  strength  of  the  amalgam. 

Professor  Black  has  shown  that  while  it  may  be  possible  to 


ALLOYS  LI  7 

stop  the  process  of  annealing  at  such  a  point  that  a  given  alloy 
will  neither  shrink  nor  expand,  it  is  easy  to  carry  the  process 
too  far  and  the  farther  it  is  allowed  to  go  the  greater  the  shrink- 
age. It  is  probably  true  that  the  exact  effect  of  annealing 
will  vary  with  the  composition  of  the  alloy,  and  with  different 
proportions  of  metals  in  alloys  of  the  same  general  composition. 

In  annealing  platinum  a  high  degree  of  heat  is  required,  but 
the  heat  should  be  raised  gradually,  and  in  this  case,  as  with 
gold,  the  electric  furnace  furnishes  an  ideal  method. 

Eutectic  Alloys.  —  The  term  eutectic  signifies  lowest  melting- 
point  or  freezing-point,  and  is  perhaps  best  illustrated  by  water 
and  salt. 

If  a  salt  solution,  so  made  that  it  contains  23.6%  by  weight 
of  sodium  chloride,  is  cooled  to  a  temperature  of  —  22°  C,  the 
two  substances  crystallize  together  in  the  form  of  a  very  intimate 
mechanical  mixture  of  ice  and  salt  crystals.  This  is  known  as 
a  eutectic  mixture  and  these  proportions,  the  eutectic  ratio 
for  salt  and  water. 

Upon  lowering  the  temperature  of  a  solution  which  contains 
less  than  23.6%  of  salt  the  excess  of  water  crystallize^  in  a  com- 
paratively pure  form,  leaving  a  brine  of  constantly  increasing 
degree  of  concentration  until  the  eutectic  proportions  are  reached. 
If  the  salt  solution  were  stronger  than  23.6%  the  salt  would  crys- 
tallize out  leaving  a  brine  of  decreasing  concentration.  Both 
of  these  latter  crystallizations  however  would  take  place  above 
—  22°  C,  so  the  point  where  the  eutectic  mixture  crystallizes 
is  the  lowest  possible  for  a  mixture  of  this  particular  nature. 

In  exactly  this  way  a  eutectic  alloy  is  one  which  has  the 
lowest  possible  melting-point  obtainable  by  use  of  the  given 
constituents;  and  in  similar  manner  also,  when  an  excess  of  one 
or  the  other  metals  is  used,  we  may  regard  the  mixture  as  a 
solution  of  the  eutectic  alloy  in  an  excess  of  metal. 

The  physical  differences  between  the  eutectic  alloy  and  "  the 
solid  solution  "  may  be  shown  by  microscopical  examination, 


Il8  DENTAL  METALLURGY 

the  eutectic  mixture  being  much  more  intimate  in  character 
than  the  other.  This  examination  is  made  by  reflected  light  upon 
a  surface  polished  as  perfectly  as  possible.  The  method  of  pro- 
cedure is  as  follows:  a  thin  piece  of  alloy  is  polished  by  the  use 
of  emery  disks  and  paper  of  varying  grades  until  the  surface 
is  as  smooth  as  possible,  then  the  poHshing  is  completed  by  the 
use  of  the  very  finest  paper,  then  by  a  rapidly  rotating  wheel 
covered  with  cloth  upon  which  jeweler's  rouge  has  been  rubbed. 
The  most  satisfactory  results  are  obtained  if  the  surface  of  the 
alloy  is  kept  wet. 

The  specimen  may  be  mounted  in  soft  wax  contained  in  a 
brass  ring  with  perfectly  parallel  edges,  as  it  is  essential  that  the 
polished  surface  be  parallel  to  the  microscope  stage.  After 
the  examination  of  the  polished  surface  it  may  be  etched  by 
various  chemicals  such  as  nitric  and  hydrochloric  acid  and  again 
examined. 


CHAPTER  XIII. 
AMALGAMS. 

In  general,  amalgams  may  be  made  in  three  different  ways: 
First,  by  direct  union  of  the  constituents,  as  in  the  manufacture 
of  sodium  amalgam  (page  121);  second,  by  electrolysis  of 
strong  solutions  of  metallic  salts  in  presence  of  mercury,  as 
in  copper  amalgam  (page  122),  and  third,  by  double  decompo- 
sition as  illustrated  in  the  preparation  of  ammonium  amalgam 
(page  121). 

The  nature  of  the  amalgam  seems  to  vary  with  the  compo- 
sition; that  is,  some  amalgams  are  apparently  true  chemical 
compounds,  others  are  solutions  of  one  metal  in  another,  or  in 
mercury,  while  still  others  are  mixtures  of  these  two,  or  solutions 
of  the  compound;  for  example  silver,  gold,  and  copper  will  form 
definite  compounds  with  mercury  from  which  the  mercury  cannot 
be  separated  by  heat  even  at  a  temperature  of  450°  C,  —  nearly 
a  hundred  degrees  in  excess  of  the  boiHng-point  of  mercury,  — 
but  these  compounds  readily  unite  with  larger  proportions  of 
mercury  in  the  formation  of  amalgams.  Also  platinum,  tin, 
cadmium,  and  bismuth  do  not  retain  mercury  at  450°  C;  and 
potassium  and  sodium  form  definite  crystalUne  compounds  with 
mercury. 

Amalgams  possess  the  peculiar  property  of  "  setting  "  or 
hardening  within  a  short  time  after  mixing.  This  in  some  cases 
seems  to  be  a  process  of  crystallization,  and  in  all  cases  is 
probably  due  to  molecular  rearrangement  of  some  sort. 

After  an  amalgam  has  "  set  "  to  a  sufficient  extent  to  make 
it  hard  to  work  it  may  be  softened  by  application  of  gentle 
heat.     Continued  reheating  is  detrimental  to  the  quaUty  of  the 

119 


I20 


DENTAL  METALLURGY 


amalgam,  and  should  be  avoided;  this  is  particularly  true  of 
copper  amalgam.  It  is  also  possible  to  sometimes  restore  the 
plastic  quality  of  an  amalgam  by  adding  a  further  sHght  amount 
of  mercury,  but  the  union  of  the  second  lot  of  mercury  after  the 
first  has  partly  hardened  is  very  unsatisfactory  and  results  in  a 
weakened  product. 

Flow  of  Amalgams.  —  This  property  may  be  defined  as  the 
tendency  to  flatten  or  change  shape  under  stress  or  pressure. 
It  is  common  to  most  amalgams  (copper  amalgam  being  an 


Fig.  9. 

exception,  according  to  Dr.  Black),  and  is  possessed  by  many 
alloys  other  than  amalgams. 

Tests  for  "  flow  "  may  be  made  with  the  "  dynamometer  " 
on  cubes  of  alloy  or  amalgam  measuring  one-tenth  of  an  inch  each 
way  and  the  results  expressed  in  percentage  of  increase  or  de- 
crease of  one  dimension.  The  dynamometer  used  for  this  pur- 
pose is  pictured  in  Fig.  9  and  is  a  modification  of  the  apparatus 
devised  by  Dr.  Black  and  described  on  pages  408  and  409  of  the 
Dental  Cosmos,  Vol.  37,  A- A  being  the  molds  in  which  the 
cubes  of  amalgams  are  set  and  B  the  point  in  the  apparatus 
where  the  cube  after  setting  is  introduced  with  a  pair  of  fine 
forceps.    The  dial  is  supplied  with  two  hands,  one  which  flies 


AMALGAMS  121 

back  the  instant  the  cube  breaks,  the  other  remaining  to  indicate 
the  number  of  pounds  applied  necessary  to  crush  the  cube. 
The  cubes  of  i/io  inch  are  best  suited  for  students'  practice, 
with  a  dial  constructed  to  record  250  pounds  pressure.  For 
accurate  comparisons  of  thoroughly  made  amalgams  the  cubes 
must  be  made  smaller. 

Binary  amalgams,  as  they  are  sometimes  called,  are  those 
consisting  of  only  one  metal  besides  mercury.  These  are  rarely 
used  in  dental  practice,  but  from  them  the  properties  of  the 
amalgamated  metal  are  most  easily  observed. 

Sodium  amalgam  may  be  made  by  direct  union  of  the  con- 
stituent elements.  The  mercury  should  be  placed  in  an  open 
dish  under  a  hood,  and  the  sodium  added  in  small  well-cleaned 
pieces. 

The  union  is  accompanied  by  a  slight  hissing  noise,  an  eleva- 
tion of  temperature  and  evolution  of  vapor  carrying  more  or 
less  mercury,  hence  dangerous  to  breathe.  An  amalgam  con- 
taining 1%  sodium  is  a  viscid  liquid;  if  it  contains  5%  sodium 
it  is  a  hard  solid  and  intermediate  percentages  give  varying 
degrees  of  firmness.  Sodium  amalgam,  if  made  with  arsenic-free 
mercury,  is  a  very  convenient  reagent  to  use  in  making 
Fleitmann's  Test  (page  35). 

Aluminium  amalgam  is  easily  made  with  aluminium  filings  and 
mercury  or  dilute  solution  of  mercuric  chloride.  This  amalgam 
decomposes  water  at  ordinary  temperatures,  gi\'ing  free  hydrogen 
and  aluminium  hydroxide. 

Ammonium  amalgam  has  no  use  in  dentistry,  but  it  is  of 
interest  in  that  it  is  the  nearest  approach  which  we  may  attain 
to  the  isolation  of ,  the  purely  hypothetical  metal  ammonium. 
It  is  easily  made  by  adding  sodium  amalgam  to  a  cold  saturated 
solution  of  ammonium  chloride,  thus  illustrating  the  third 
general  method  of  preparation  of  amalgams.  It  rapidly  decom- 
poses at  ordinary  temperature  with  the  Hberation  of  free  hydro- 
gen ammonia-gas  and  metallic  mercury.     The  hydrogen  thus 


122  DENTAL  METALLURGY' 

liberated  exhibits  the  properties  of  nascent  hydrogen,  indicating 
that  in  the  amalgam  it  existed  in  true  chemical  combination,  that 
is  NH4,  rather  than  in  any  physical  solution.  At  ordinary  tem- 
perature ammonium  amalgam  is  a  soft,  pasty,  very  porous 
mass,  but  at  much  reduced  temperature  it  becomes  solid  and 
crystalline,  although  at  —  39°  (the  freezing-point  of  mercury) 
hydrogen  and  NH3  are  still  given  off. 

Copper  amalgam  is  by  far  the  most  valuable  of  this  class 
of  amalgams.  It  may  be  made  by  amalgamating  precipitated 
copper  after  moistening  it  with  nitrate  of  mercury  (Essig). 
The  precipitated  copper  may  be  prepared  by  action  of  metallic 
zinc  in  a  sHghtly  acid  copper  sulphate  solution,  but  must  be 
thoroughly  washed  with  hot  water  to  free  it  from  zinc  chloride. 
The  amalgamation  may  be  effected  by  use  of  mortar  and  pestle. 
Rollins'  method  *  by  electrolysis  of  strong  copper  sulphate  solu- 
tion is  rather  unwieldly,  but  illustrates  very  well  the  second 
general  process  for  the  manufacture  of  amalgams. 

Copper  amalgam,  according  to  Black,  is  absolutely  rigid 
after  it  has  once  set  and  does  not  flow  even  to  a  slight  extent. 
It  is  fine-grained  and  very  hard.  It  is  reduced  in  strength  by 
reheating  and  does  not  expand  or  contract.  In  the  mouth  copper 
amalgam  dissolves  with  comparative  rapidity  owing  to  the 
ready  formation  first  of  copper  sulphide,  then,  by  the  oxidation  of 
this  compound,  of  the  sulphate.  It  blackens  rapidly  and  in 
consequence  of  the  tendency  just  mentioned,  to  dissolve,  it  may 
penetrate  the  dentine  and  thus  discolor  the  tooth  itself. 

Gold  amalgam  is  readily  made,  but  does  not,  by  itself,  harden 
well.  An  amalgam  containing  one  part  of  gold  to  six  of  mercury 
will  crystallize  in  four-sided  prisms  (Litch) . 

Magnesium  amalgam  may  be  easily  produced,  but  like 
the  amalgams  with  aluminium  or  sodium  it  decomposes  water 
with  the  evolution  of  hydrogen. 

*  Details  of  this  method  may  be  found  in  the  Boston  Medical  and  Surgical 
Journal,  February,  1886;  also  in  Mitchell's  Dental  Chemistry. 


AMALGAMS  123 

Platinum  amalgam  is  very  smooth,  is  formed  with  difficulty 
unless  the  platinum  is  very  llnely  divided,  and,  like  gold,  does  not. 
harden  well. 

Silver  amalgam,  easily  made  but  tends  to  expand. 

Tin  amalgam,  alone,  shrinks  badly. 

Zinc  amalgam,  readily  made,  is  white,  but  too  brittle  to  be  of 
service. 

Cadmium  amalgam  may  be  easily  made  at  ordinary  tem- 
perature, "  sets  quickly,  and  resists  sufficiently,  but  fillings  con- 
taining it  gradually  soften  and  disintegrate  and  may  stain 
the  dentine  bright  yellow  by  formation  of  cadmium  sulphide." 
(Mitchell.) 

Effect  of  Various  Metals  in  Amalgam  Alloys. 

With  the  properties  of  these  simpler  combinations  before 
us  it  becomes  easy  to  understand  the  effect  the  addition  of  the 
various  metals  will  have  upon  the  properties  of  a  silver- tin 
alloy;  for  practically  all  amalgam  alloys  are  silver- tin  alloys, 
either  simple  or  combined  with  one  or  more  other  metals. 

Silver  and  tin  are  the  most  valuable  constituents  of  amalgam 
alloys.  Silver  is  essential  to  the  proper  setting  and  hardening 
of  the  amalgam.  It  tends  to  increase  expansion  and  to  hasten 
setting,  while  tin  possesses  the  opposite  characteristics.  Com- 
bined with  tin  in  the  proportion  of  65%  silver  to  35%  tin,  it 
forms  an  amalgam  alloy  perhaps  more  largely  used  than  any 
other.  It  was  this  combination  that  Dr.  Black  succeeded  in 
"  annealing  to  zero,"  that  is,  so  that  upon  testing  it  showed 
neither  expansion  nor  contraction. 

Pure  silver- tin  allo3^s  will  flow  from  2.5  to  10%. 

Dr.  C.  M.  McCauley  in  an  article  on  amalgams  published 
in  the  Dental  Cosmos  for  February,  191 2,  states  that  the  formula 
of  65%  silver  and  35%  tin  will  produce  an  amalgam  which  gives 
no  shrinkage  if  the  freshly  cut  alloy  is  used,  but  upon  anneaHng 
the  alloy  it  was  necessary  to  use  about  74%  silver.     He  further 


124  DENTAL   METALLURGY 

states  that  5%  of  copper  for  an  equivalent  of  silver  increases 
the  strength  of  amalgams  made  from  silver-tin  alloys. 

Dr.  McCauley  also  tells  us  that  a  contraction  of  one  ten- 
thousandth  of  an  inch  will  admit  organisms  producing  caries 
into  a  tooth  cavity,  but  that  the  expansion  of  the  finished  filling 
of  about  one  twenty-thousandth  of  an  inch  is  a  desirable  result. 

The  larger  the  proportion  of  tin  the  easier  will  the  alloy 
cut,  but  the  coarser  will  be  the  filings. 

Zinc  added  to  a  silver-tin  alloy  tends  to  whiten  the  amalgam, 
hastens  setting,  increases  the  flow,  and,  according  to  Essig, 
"  causes  a  great  but  slow  expansion." 

Dr.  McCauley,  quoted  above,  states  that  zinc  is  unfavor- 
able in  its  action  on  other  metals  in  a  dental  alloy  and  detrimental 
when  used  to  the  extent  of  only  one  per  cent,  because  of  its  ■ 
tendency  to  produce  a  constant  expansion  for  several  months, 
even  though  tests  made  during  the  first  few  days  were  satis- 
factory. 

Cadmium,  see  page  123. 

Antimony  gives  a  fine  grain  alloy  and  when  the  silver  is  less 
than  50%  is  supposed  to  control  shrinkage. 

Bismuth  will  increase  the  flow  of  the  amalgam;  it  is  some- 
times used  in  low-grade  silver- tin  alloys  to  control  shrinkage. 

Copper  tends  to  diminish  flow  and  gives  a  strength  under 
pressure,  sets  quickly,  gives  better  margins,  and  by  some  is 
believed  to  have  preservative  influence  on  the  tooth  substance, 
but  the  more  copper  in  an  alloy  the  more  rapidly  does  it  dis- 
color. 

Gold.  —  From  three  to  seven  per  cent,  of  gold  in  a  silver-tin 
alloy  diminishes  shrinkage,  helps  the  color  and  adds  to  crush- 
ing strength.     The  filing  from  such  an  alloy  will  be  very  fine. 

Dr.  Black  says  5%  of  gold  gives  a  softer  working  property 
but  retards  setting  of  the  amalgam,  and  makes  it  otherwise 
difficult  to  give  a  good  finish  to  the  filHng  (Dental  Cosmos, 
Vol.  38,  page  988). 


AMALGAMS 


125 


Platinum  according  to  Black,  is  not  a  desirable  addition 
to  a  silver-tin  alloy.  It  gives  an  alloy  furnishing  very  fine  filing, 
which  produces  a  dirty  working,  slow-setting  amalgam. 

Excess  of  Mercury.  —  In  the  preparation  of  an  amalgam 
from  a  dental  alloy  it  is  usual  to  add  more  mercury  than  the 
finished  product  requires  and  then  squeeze  out  the  excess  be- 
tween the  lingers  or  otherwise.  In  filling  a  cavity,  still  more 
mercury  is  forced  out,  so  that  the  composition  of  the  deeper 
portions  of  a  filling  varies  from  the  outer  portions  and  probably 
accounts  for  the  inequalities  in  expansion  or  contraction.  The 
excess  of  mercury  from  the  surface  of  a  filHng  may  be  absorbed  by 
a  Httle  hot  gold  or  pure  tin  or  by  finely-divided  silver. 

Following  is  a  short  Hst  of  dental  alloys,  most  of  which  may 
be  easily  prepared: 


Arington's  (S.  S.  White's) 

*(C.  A.  S.)  alloy,  C.  Ash  Sons  Co.. 

Chase  copper-amalgam  alloy 

Chase's  incisor  alloy 

*Fellowship  alloy 

Flagg's  submarine  alloy 

Fletcher's  gold  alloy  (old) 

High-grade  alloy  (7!%  gold) 

Harris's  amalgam  alloy 

King's  occidental  alloy 

*Odontographic  alloy .  .  . 

*Standard  alloy 

Standard  dental  alloy  (Eckfeldt) . 

60%  silver  alloy 

Temporary  alloy 

*True  dentalloy 

*Twentieth  century 


Sn 


Ag        Au 


42.5 
56.54 
50 
50 

67-45 

60 

40 

49 
40 

42.75 

66.87 

53-55 

52 

60 

10 

65-91 
67.03 


4 
7-5 


0.28 
8.82 
4-4 


Cu 


5-o: 


5-73 
5 


4-9 

6.21 
2.76 
3 


5.21 
4.87 


Zn       Sb 


0.90 
0-S5 


7 

2.5 
trace 


I-S2 
I  .10 


*  Analyses  by  Dr.  P.  J.  Burns  of  the  Mass.  Inst.  Technology,  reported  in 
the  Journal  of  the  Allied  Societies,  June,  1908. 

These  formulae  have  been  selected  from  various  sources  with 
a  view  to  giving  the  student  opportunity  to  study  effects  ob- 
tained by  varying  percentages  of  tin  and  silver,  and  by  introduc- 
tion of  other  metals,  copper,  zinc,  etc. 


126  DENTAL  METALLURGY 

The  excess  of  mercury  which  has  to  be  squeezed  out  of  an 
amalgam  carries  with  it  more  or  less  of  the  constituent  metals. 
Hall  found  that  whatever  the  amount  of  mercury  expressed,  it 
carried  just  about  i%  of  tin.  In  the  author's  experience  this 
amount  has  reached  nearly  if%  of  tin.  Silver  is  carried  out  to 
a  much  less  extent  than  tin,  so  it  is  not  impossible  to  carelessly 
make  an  amalgam  and  squeeze  out  enough  mercury  to  change 
the  proportion  of  silver  and  tin  in  the  alloy.  This  change  will, 
of  course,  be  very  sUght,  but  we  have  seen  that  the  contraction 
and  expansion  of  amalgams  may  be  affected  by  slight  changes  in 
composition. 

Tests  for  Amalgams. 

Color  Test.  —  This  is  made  upon  a  freshly  amalgamated 
alloy,  rolled  into  about  the  shape  and  size  of  a  small  pea,  with 
a  view  to  determine  the  amount  of  discoloration  the  amalgam 
is  liable  to  undergo  in  the  mouth. 

A  ball  of  amalgam  carefully  smoothed  on  at  least  one  side 
is  placed  for  forty-eight  hours  in  a  saturated  solution  of  hydro- 
gen sulphide,  and  after  that  time  its  color  is  compared  with  other 
amalgams  similarly  treated,  or  with  amalgam  of  a  similar  com- 
position which  has  not  been  treated. 

Test  for  Expansion  or  Contraction. 

Black  has  shown  that  tests  of  this  nature  to  be  of  any  value 
must  be  made  in  such  a  way  that  the  amount  of  change  in  the 
volume  can  be  measured,  and  that  the  simple  method  of  pack- 
ing glass  tubes  and  using  colored  ink  is  wholly  unreliable. 

The  author  uses  for  this  purpose  an  apparatus  similar  to 
one  described  by  Prof.  Vernon  J.  Hall.  The  amalgam  is  packed 
closely  into  a  "  well  "  in  a  steel  block,  then  the  block  is- placed 
in  the  apparatus  so  that  a  counterpoised  steel  plunger  rests  on 
the  column  of  amalgam.  This  plunger  is  operated  by  a  very 
long  needle  and  attached  at  a  point  so  near  the  pivotal  support 


AMALGAMS 


127 


of  the  needle  that  a  rise  or  fall  of  the  plunger  of  1/2500  of  an 
inch  moves  the  tip  of  the  needle,  at  the  scale,  1/16  of  an  inch, 
or  one  degree.  If  the  needle  rises  half  a  degree,  which  may 
easily  be  read,  it  would  indicate  an  expansion  of  the  amalgam 
of  I  5000  of  an  inch. 

There  are  two  wells  in  each  block  and  both  of  exactly  the 
same  depth.  The  figure  given  below  will  make  this  explanation 
easily  understood.  A  being  the  steel  block  carr}-ing  the  amalgam. 


Fig.  10. 

Test  for  Crushing  Strength  and  Flow.  —  The  test  is  made 
with  Dr.  Black's  dynamometer  (page  120)  upon  cubical  blocks 
of  amalgam  which  have  been  allowed  to  "  set  "  for  at  least  two 
days,  and  which  measure  i   10  of  an  inch  each  way.   . 

Specific  gravity  may  be  obtained  by  weighing  the  sample 
fijst  in  water,  then  in  air.  and  di\'iding  the  weight  in  air  by  the 
difi'erence  between  the  two  weights  obtained. 

It  is  instructive  to  make  these  tests  on  amalgam  from  aUoys 
of  varsing  composition,  also  on  annealed  and  unannealed  aUoys 
of  the  same  composition. 


CHAPTER  XIV. 
FUSIBLE   METALS   AND   SOLDERS. 

Fusible  Metals. 

Under  the  head  of  fusible  alloys  properly  come  many  of 
the  alloys  considered  on  page  129  as  solders.  The  fusible  alloy 
usually  contains  lead  or  bismuth  together  with  tin  and  occasion- 
ally cadmium.  This  may  be  mixed  in  such  proportions  that 
the  melting-point  may  be  anything  desired  down  to  63°  C. 
These  alloys  are  largely  used  in'  the  dental  laboratory.  Mellot's 
metal,  composed  of  bismuth  eight  parts,  tin  five  parts,  and  lead 
three  parts,  is  perhaps  the  most  serviceable.  This  melts  at  about 
the  temperature  of  boihng  water.  Wood's  metal,  melting  at 
about  65°  C,  is  composed  of  bismuth  four  parts,  tin  one,  lead 
two  and  cadmium  one.  Rose's  metal  is  bismuth  two  parts, 
tin  one,  and  lead  one.     This  melts  at  about  95°  C. 

Babbitt  Metal,  much  used  in  the  manufacture  of  dies,  is 
composed  of  copper  one  part,  antimony  two,  and  tin  eight.  The 
formula  of  common  Babbitt  metal  on  the  market  will  be  found 
to  differ  somewhat  from  the  above  and  is  not  so  well  suited  for 
dental  purposes. 

According  to  Essig's  Dental  Metallurgy,  Dr.  C.  M.  Rich- 
mond used  a  fusible  alloy  in  crown  and  bridge  work  which  he 
states  is  as  hard  as  zinc  and  can  be  melted  at  150°  F.  and  poured 
into  a  plaster  impression  ^^^thout  generating  steam.  The  for- 
mula of  this  alloy  is  as  follows:  Tin  twenty  parts,  lead  nineteen, 
cadmium  thirteen,  and  bismuth  forty-eight.  The  following 
fusible-metal  alloys  are  also  suitable  for  the  purpose. 

Tin.  Lead.  Bismuth.  Melting-point  of  Alloy. 

12  2  236°  F.  or  113°  C. 

S     •  3  3  202°  F.  or    94°  C. 

358  197°  F.  or    92°  C. 

128 


FUSIBLE   METALS  yiND  SOLDERS 


129 


The  fusing-point  of  an  alloy  may  be  determined  by  melting 
under  a  liquid  of  sufficiently  high  boiling-point  and  then  care- 
fully noting  the  temperature  at  which  the  melted  alloy  solidities. 

Approximate  results  may  be  obtained  by  watching  care- 
fully the  melting  of  a  very  thin  strip  of  alloy. 

Care  must  be  taken  that  the  temperature  of  the  alloy  is 
exactly  the  same  as  recorded  by  the  thermometer.  To  insure  this 
in  the  case  of  an  alloy  with  low 
melting-point,  it  is  usually  sufficient 
to  place  the  alloy  in  water  or  brine 
in  a  test-tube  which  is  immersed  in 
a  beaker  of  similar  fluid,  then,  by 
raising  the  heat  gradually  with  con- 
stant stirring  and  by  taking  the 
mean  of  two  or  three  determina- 
tions, fairly  accurate  results  are 
obtained. 

Solders. 


Solders  are  alloys  used  in  join- 
ing pieces  of  metal  of  the  same  or 
of  different  kinds.  One  of  the  con- 
stituent metals  of  the  alloy  forming 
the  solder  is  usually  the  same  as 
the  surface  upon  which  it  is  to  be 
used,  hence  the  various  metals  re- 
quire solders  of  special  composition;  for  instance,  common  sol- 
der is  entirely  unsuited  for  soldering  aluminium  or  gold. 

Common  Solder  is  composed  of  tin  and  lead  in  different 
proportions.  The  larger  the  proportion  of  tin  the  finer  is  the 
solder,  and  the  following  three  grades  may  usually  be  obtained: 
"  Fine  "  or  "hard  "  (tin  two  parts  and  lead  one),  "  Common  "  or 
"  medium  "  (tin  and  lead  equal  parts),  "  Coarse  "  or  "  soft  " 
(tin  one  part  and  lead  two  parts) . 


Fig.  II.  —  Apparatus  for  Taking 
Melting-Point. 


130  DENTAL  METALLURGY 

In  soldering  metals,  it  is  absolutely  essential  that  the  sur- 
faces be  kept  clean  and  free  from  superficial  coating  of  oxides 
which  may  form  easily  with  the  elevated  temperature  employed 
in  the  process.  Soldering  acid  and  the  various  fluxes  serve  this 
purpose.  Soldering  acid  is  an  acid  solution  of  zinc  chloride 
usually  made  by  taking  a  few  ounces  of  strong  hydrochloric 
acid  and  adding  zinc  as  long  as  the  metal  dissolves.  Among 
the  substances  which  may  be  used  as  a  flux  to  prevent  oxidation, 
rosin  and  borax  are  the  most  common. 

Soft  Solders  are  those  fusing  below  a  red  heat  and  include 
the  common  solders  above  mentioned,  also  the  most  fusible 
solders  containing  bismuth.  These  last  are  more  properly 
fusible  metals  and  are  discussed  under  that  head. 

Solders  for  Aluminium.  —  Aluminium  solders  with  consider- 
able difficulty  owing  in  part  to  the  low  melting-point  of  the 
metal,  also  to  the  fact  that  aluminium  is  attacked  by  alkalis, 
.including  borax,  which  makes  it  necessary  to  find  some  sub- 
stitute for  this  convenient  flux.  Essig  recommends  a  flux  con- 
sisting of  three  parts  of  copaiba  balsam,  one  part  of  Venetian 
turpentine,  and  a  few  drops  of  lemon-juice.  The  mixture  is  to 
be  used  in  the  same  manner  as  soldering  acid  with  a  solder  con- 
sisting of  zinc  from  eighty  to  ninety-two  parts,  aluminium  from 
eight  to  twenty  parts.  Fused  and  finely  powdered  silver  chlo- 
ride may  also  be  used  as  a  flux,  the  salt  being  reduced  and  the 
silver  forming  a  superficial  alloy.  Richards  recomnkends  a 
solder  for  aluminium  consisting  of  tin  twenty-nine  parts,  zinc 
eleven  parts,  aluminium  one  part,  phosphor-tin  one  part. 

Hall  says  that  a  solder  which  he  has  found  very  satisfactory 
may  be  prepared  from  aluminium-  forty-five  parts,  tin  forty-five, 
mercury  ten;  further,  that  the  following  formulae  suggested  by 
Schlosser  are  particularly  adapted  to  soldering  dental  work 
since  they  resist  the  reaction  of  corrosive  substances. 


FUSIBLE  METALS  AND  SOLDERS 


131 


Platinum-Aluminium 
Solder. 

Gold 3 .    parts 

Platinum o .  i  part 

Silver 2      parts 

Aluminium 10       " 


Gold-Aluminium 
Solder. 

Gold 5  parts 

Copper I  part 

Silver I     " 

Aluminium 2  parts 


For  soldering  articles  of  aluminium  the  following  solder  is 
given  in  the  Phaniiaceutical  Era,  January  10,  1895:  Silver  two, 
nickel  five,  aluminium  nine,  tin  thirty-four,  and  zinc  fifty  parts, 
to  be  used  without  flux.     See  also  Dental  Cosmos  for  1906  (page 

115)- 

Solder  for  Brass  requires  a  high  heat  for  fusion  and  on  this 
account  is  known  as  hard  solder. 

Edwinson  gives  the  following  formulas:  (i)  copper  thirteen 
parts,  silver  eleven;  (2)  copper  one  part,  brass  one,  silver  nine- 
teen; (3)  brass  five  parts,  zinc  five,  silver  five.  The  flux  for 
brass  soldering  is  powdered  borax,  which  may  be  mixed  with 
water  to  a  paste  and  appHed  with  a  feather  or  a  small  brush. 

Solder  for  Gold.  —  Gold  soldering  is  the  most  particular 
work  of  this  class  which  the  dentist  has  to  do.  There  are  a 
few  requirements  for  a  good  gold  solder  which  might  be  noted 
and  which  are  also  applicable  to  the  other  solders  mentioned: 
(i)  The  color  should  be  as  nearly  as  possible  that  of  the  metals 
upon  which  it  is  to  be  used.  (2)  The  solder  should  have  a 
fusing-point  but  very  sHghtly  below  that  of  the  metal  to  be  sol- 
dered.    (3)  The  solder  should  flow  freely. 

Litch  gives  the  following  instructions  for  making  a  zinc-gold 
solder  which  will  have  the  above-mentioned  properties: 

"  To  make  the  zinc-gold  solder  take  one  pennyweight  of  the 
same  gold  upon  which  it  is  to  be  used  and  add  one  and  a  half 
grains  of  zinc.  If  this  is  done  in  a  crucible  in  the  furnace,  first 
fuse  the  gold  (which  should  either  be  clean  scraps  or  be  cut 
from  the  plate;  never  use  fihngs  for  this  purpose),  using  but  Httle 
borax;  when  thoroughly  fused  take  the  crucible  in  the  tongs, 
drop  the  zinc  into  it,  give  the  crucible  a  rather  vigorous  yet 


132  DENTAL  METALLURGY 

skilful  shake  to  assist  in  mixing  its  contents,  but  without  causing 
any  to  be  thrown  out,  and  immediately  pour  into  the  previously 
prepared  ingot  mold.  This  must  be  done  very  quickly  or  the 
solder  will  require  too  high  a  heat  for  the  fusion  on  account  of 
a  large  proportion  of  the  zinc  being  volatilized  or  oxidized  and 
thus  be  lost  as  alloys." 

Essig  gives  the  following  formulae  for  alloys  of  gold  employed 
in  dentistry  as  solders: 

No.  I.     14  Carats  Fine.  No.  2.     14  Carats  Fine. 

American  gold  coin $10.00  American  gold  coin.     16  dwts. 

Pure  silver 4  dwts.  Pure  copper 3        "       18  grs. 

Pure  copper 2      "  Pure  silver 5        " 

No.  3.     14  Carats  Fine.  No.  4.     15  Carats  Fine. 

Pure  silver 25  dwts.  Gold  coin 6    dwts. 

Pure  copper 20  grs.  Pure  silver 30    grs. 

Pure  zinc 35     "  Pure  copper 20      " 

i8-carat  gold  plate   (formula  Brass 10      " 

No.  11) 20    dwts. 

No.  5.     16  Carats  Fine.  No.  6.     16  Carats  Fine. 

Pure  gold 11  dwts.  Pure  gold ii  dwts.  12  grs. 

Pure  silver.    3      "      6  grs.        Pure  copper i  dwt.    12     " 

Pure  copper 2      "     6    "  Pure  silver 3  dwts. 

Pure  zinc. 12  grs. 

No.  7.     18  Carats  Fine. 

Gold  coin 3°  parts 

Pure  silver 4 

Pure  copper i  part 

Brass i 

No.  8.     20  Carats  Fine,  for  Crown  and  Bridge  Work. 

American  gold  coin  (21.6  carats  fine)  $10  piece 258        grs. 

Spelter  solder 20 .  64    " 

No.  9.     20  Carats  Fine,  Same  Use  as  No.  8. 

Pure  gold 5    dwts. 

Pure  copper 6    grs. 

Pure  silver 12 

Spelter  solder 6 


FUSIBLE  METALS  AND  SOLDERS  135 

No.  10.     20  Carats  Fixe,  for  Crown  and  Brtoge  Work. 

Zinc 1 3   grs. 

Pure  gold 20        " 

Silver  solder 3       " 

No.  II.     Dr.  C.  M.  Richmond's  Solder  for  Bridge  Work. 

Gold  coin 5   dwts. 

Fine  brass  wire i    dwt. 

No.  12.  Dr.  Low's  Formltla  for  Solder  for  Crown  and  Bridge 
Work,  19  C.'VR.\ts  Fine. 

Coin  gold I     dwt. 

Copper 2      grs. 

Silver 4        " 

Solder  for  Platinum.  —  Platinum  utensils  may  be  soldered 
with  any  good  gold  solder,  and  a  iiux  may  be  used  if  desired. 
WTien,  however,  the  solder  is  used  in  connection  with  porcelain 
work,  it  must  be  pure  gold  or  a  gold  and  platinum  alloy.  A 
twenty-five  per  cent,  platinum  alloy  has  been  found  to  give  ex- 
cellent results.  The  followang  in  regard  to  gold  and  platinum 
alloy  is  from  the  Dental  Review,  August,  1905: 

"  The  colleges  and  text-books  tell  us  the  proper  proportions  of 
gold  and  platinum  alloys,  but  they  usually  fail  to  tell  us  how 
to  do  it.  In  most  cases  the  platinum  appears  in  white  spots 
on  the  plate  \nthout  producing  a  proper  alloy.  Take  a  small 
piece  of  twenty-two-carat  gold  and  fuse  it  under  the  blowpipe. 
Then  work  in  all  the  platinum  you  can  in  small  pieces  until  it 
has  taken  up  all  that  is  required.  It  will  produce  a  small  button 
of  a  white  aUoy  which  is  very  brittle.  Add  this  alloy  in  required 
proportions  to  the  gold  in  the  crucible  and  it  wall  produce  a  real 
platinimi  alloy.  By  this  method  you  can  make  clasp  gold  that 
is  pretty  nearly  as  stiff  as  a  steel  spring  and  yet  will  roU  and  work 
without  fracture."     (Mark  G.  IMcElhinney,  Ottawa,  Canada.) 

Solder  for  Silver.  —  Solder  for  silver  usually  consists  of 
alloys  of  silver  and  copper  with  sometimes  zinc  and  sometimes 
tin.     Litch  recommends  a  silver  solder  made  by  alloying  pure 


134  DENTAL   METALLURGY 

silver  with  one-third  its  weight  of  brass.  "  Brannt's  Metallic 
Alloys  "  gives  alloys  of  silver  and  copper  simply.  Hall  recom- 
mends silver  eight  parts,  copper  one,  and  zinc  two.  In  the 
preparation  of  solder  containing  copper,  zinc,  or  tin,  the  use  of 
a  flux  is  necessary  to  prevent  the  formation  of  metallic  oxide. 
For  this  purpose  borax  is  usually  employed.  The  silver,  con- 
stituting, as  it  does,  the  greater  proportion  of  the  alloy,  should 
be  melted  first  and  be  covered  with  considerable  borax.  When 
this  has  been  thoroughly  fused,  the  other  metals  may  be  added 
and  mixed  by  agitation  or  by  stirring  with  wood.  Finally,  the 
solder  may  be  cast  in  the  usual  ingot  moid. 


CHAPTER  XV. 
DENTAL   CEMENTS. 

Dental  Cements  may  be  classified  as  ordinary  oxyphosphates 
of  zinc  cements,  copper  cements  and  synthetic  cements  which 
include  the  artificial  enamels.  These  three  kinds  will  include 
by  far  the  larger  proportion  of  cements  in  common  use,  and  all 
contain  more  or  less  oxyphosphate  of  zinc. 

Ox3rphosphate  of  Zinc.  —  The  oxyphosphate  cement  is 
usually  made  by  adding  a  powder,  consisting  largely  of  pure 
oxide  of  zinc,  colored  by  a  sUght  amount  of  other  metallic  ox- 
ides, to  a  liquid  consisting  of  deliquesced  phosphoric  acid  (or 
a  solution  of  phosphoric  acid  in  which  zinc  phosphate,  and 
possibly  slight  amounts  of  other  phosphates,  have  been  dissolved) , 
till  a  putty-like  mass  results,  which  rapidly  hardens  and  becomes 
capable  of  receiving  a  considerable  poHsh.  When  the  phosphoric 
acid  used  is  the  glacial  acid,  the  cement  may  be  spoken  of  as  a 
metaphosphate,  because  the  glacial  acid,  before  the  addition  of 
water,  and  to  a  certain  extent  afterwards,  is  actually  metaphos- 
phoric  acid,  HPO3.  The  metaphosphoric  acid  by  boiling  with 
water  or  gradually  by  addition  of  water  without  boiHng  becomes 
the  orthophosphoric  acid  (H3PO4). 

Hall's  Dental  Chemistry  takes  the  following  tests  from 
Flagg's  Plastics  and  Plastic.  Filling,  as  characterizing  a  good 
oxyphosphate  cement. 

General  Tests,  i .  When  first  mixed  it  should  yield  a  tough 
mass  which  when  removed  from  the  spatula  does  not  adhere 
to  the  fingers  and  can  be  roUed  into  a  pHable  pellet. 

135 


136  DENTAL  METALLURGY 

2.  It  should  have  a  glassy  surface;  and,  at  the  end  of  two 
or  three  minutes,  it  should  rebound  when  dropped  upon  wood, 
glass,  or  porcelain. 

3.  At  the  end  of  five  minutes  it  should  be  quite  hard  and 
should  sound  like  porcelain  when  tapped. 

4.  After  ten  or  fifteen  minutes  it  should  be  dented  with 
difficulty,  and  when  broken  should  show  a  clean,  sharp  fracture. 

5.  After  twenty  minutes  it  should  be  very  hard,  and  should 
be  capable  of  taking  a  good  burnish. 

6.  In  thirty  minutes  it  should  have  little  or  no  acid  taste. 

Arsenic  is  a  frequent  impurity  in  both  zinc  oxide  and  phos- 
phoric acid,  and  if  present  is  very  Hable  to  produce  an  irri- 
tating cement,  sometimes  causing  considerable  trouble;  hence, 
the  material  entering  into  the  composition  of  any  dental 
cement  should  be  free  from  arsenic  (see  pages  34  to  38  for  arsenic 
tests) . 

The  purer  the  zinc  oxide  and  the  phosphoric  acid,  from  which 
the  cement  is  made,  the  more  durable  it  is  found  to  be;  so,  aside 
from  any  question  of  irritation,  it  is  quite  necessary  for  the  sake 
of  the  cement  itself  that  the  ingredients  be  pure. 

It  is  not  intended  to  give  the  impression  that  the  liquid  should 
consist  only  of  glacial  phosphoric  acid  or  the  powder  only  of  oxide 
of  zinc.  A  cement  thus  made  would  set  so  rapidly  that  it  would 
be  of  no  practical  value.  The  resulting  mass  would  also  prob- 
ably be  crumbly.  The  powder  or  the  hquid,  one  or  the  other, 
is  usually  mixed  with  phosphates  of  the  heavy  metals  which 
would  be  insoluble  in  water,  but  which  would  dissolve  in  the 
strong  phosphoric  acid. 

A  pure  zinc  oxide  may  be  made  by  calcining  the  precipitated 
carbonate  of  zinc,  Zn5(OH)6(C03)2  +  heat  =  5  ZnO  +  2  CQ2  + 
3  H2O.  The  heat  should  be  below  500°  F.,  because,  if  too  strongly 
heated,  the  color  suffers,  becoming  yellowish. 

Another  method  of  making  pure  oxide  of  zinc  is  given  as 
follows:   Dissolve  pure  zinc  in  nitric  acid,  evaporate  to  dryness, 


DENTAL  CEMENTS  1 37 

and  heat  till  fumes  cease  to  be  given  off.  The  mechanical  effect 
of  the  escaping  oxides  of  nitrogen  is  said  to  leave  the  zinc  oxide 
in  the  form  of  a  very  fine  powder. 

A  pure  phosphoric  acid  can  be  made  from  the  ortho-acid 
by  heating  till  the  white  fumes  begin  to  come  off,  then  heating 
to  redness,  cooling  and  dissolving  in  water  to  a  thick  syrup.  In 
mixing  cements,  the  powder  should  be  worked  into  the  Uquid 
till  the  desired  consistency  is  obtained. 

Ox>phosphate  cement  and  all  cements  having  zinc  oxide  for 
a  base  tend  to  dissolve  in  the  fluids  of  the  mouth,  lactic  acid  and 
ammonium  salts  being  particularly  good  solvents  for  this  class 
of  compounds.  The  addition  of  ferric  oxide  to  oxyphosphate 
cement  increases  resistance  to  disintegration.  One  part  of 
ferric  oxide  to  six  to  ten  of  zinc  oxide  is  recommended  by  Rollins 
in  the  International  Dental  Journal. 

Oxychloride  of  Zinc  is  more  easily  soluble  than  oxyphos- 
phate. It  shrinks  more,  but  is  credited  with  a  preservative 
action  on  dentine  and  hence  is  used  to  some  extent  as  a  lining. 

The  powder  of  the  oxychloride  cement  is  zinc  oxide  with 
sometimes  a  little  borax,  or  silica,  or  both,  added.  A  good 
oxychloride  cement  'wt.11  set  in  fifteen  or  twenty  minutes,  but 
keeps  on  groT;\ang  harder  for  several  hours.  The  following 
formula  is  recommended. 

,  Oxide  of  zinc  10  grams,  borax  o.i  gram,  and  powdered  sihca, 
0.2  gram.  . 

Transfer  to  clay  crucible  and  calcine  for  one-half  hour  in 
furnace  at  bright-red  heat.  Pulverize,  sift,  and  bottle.  The 
liquid  to  be  used  with  this  powder  consists  of  10  c.c.  of  pure 
hydrochloric  acid  saturated  with  pure  zinc  and  filtered  through 
glass  wool.  ^  . 

Oxysulphate  of  Zinc.  —  This  is  used  still  less  than  the  oxy- 
chloride. It  is  non-irritating,  dissolves  easily,  and  is  compara- 
tively soft.  The  following  formula  is  taken  from  Hall's  Dental 
Chemistry. 


138  DENTAL  METALLURGY 

Ten  grams  oxide  of  zinc,  four  grams  sulphate  of  zinc.  Dry, 
mix,  calcine  for  one-half  hour,  and  sift. 

Liquid  to  be  used  with  the  powder  may  be  made  by  dissolv- 
ing two  grams  of  zinc  chloride  in  10  c.c.  of  water.  This  gives  a 
turbid  solution  and  should  be  shaken  when  used. 

Oxyphosphate  of  Copper  cement  (Ames's)  consists  of  the 
usual  powder  and  liquid.  The  powder  contains  oxides  of  cop- 
per, iron  (sHght  amount),  cobalt,  and  zinc,  and,  of  course,  is 
black  in  color.  The  liquid  is  phosphoric  acid  holding  in  solution 
a  certain  amount  of  phosphate  of  zinc. 

The  cement  resulting  from  this  combination  was  found  to 
be  hard,  showdng  practically  no  change  of  volume  and  resisting 
the  solvent  action  of  the  saliva. 

White  Copper  cement.  The  powder  of  this  preparation  has 
been  found  to  consist  of  95%  oxide  of  zinc  and  5%  of  cuprous 
iodide.*  The  presence  of  iofline  can  be  easily  demonstrated 
by  treatment  with  nitric  acid  and  the  solution  of  the  iodine  in 
chloroform. 

Tin  cement.  Dr.  Arthur  Scheuer,  of  Teplitz,  Bohemia,  recom- 
mends a  preparation  composed  of  a  finely  pulverized  tin  sponge 
and  zinc  oxide  mixed  with  glacial  phosphoric  acid.  "  The  powder 
is  of  a  light-gray  color,  becoming  slightly  darker  when  mixed  with 
the  acid,  but  regains  its  original  color  after  setting.  A  tin- 
cement  filling  can  be  easily  inserted  and  when  poHshed  it  has  a 
metallic  appearance."     (Dental  Cosmos,  May,  1904.) 

Artificial  Enamel.  —  Several  preparations  have  been  put  on 
the  market  under  this  name,  in  each  case  with  the  claim  that  it 
makes  a  much  harder  cement  and  one  which  resists  disintegra- 
tion to  a  much  greater  extent  than  the  ordinary  zinc  preparations. 

The  specifications  of  a  German  patent,  under  which  one  of 
these  preparations  is  manufactured,  claim  that  the  powder  con- 
sists of  a  mixture  of  the  oxides  of  beryllium  and  siHcon,  together 
with  alumina  and  lime.     The  hquid  consists  of  a  50%  solution 

*  W.  V.  B.  Ames,  D.D.S.,  Dental  Review,  June,  1914. 


DENTAL  CEMENTS  139 

of  orthophosphoric  acid  in  which  aluminium  phosphate  and 
zinc  phosphate  have  been  dissolved. 

A  qualitative  analysis  confirms  the  claim  of  the  patent  spe- 
cifications both  in  regard  to  the  composition  of  the  liquid  and 
the  presence  of  oxide  of  beryllium  in  the  powder,  and  it  is  prob- 
able that  the  value  of  these  preparations  depends  largely  upon 
the  proportion  of  beryllium  entering  into   their  composition. 

This  statement  from  an  earlier  edition  has  been  quoted* 
with  the  assertion  that  about  one-quarter  of  the  powder  of 
Ascher's  artificial  enamel  is  beryllium  oxide. 

Beryllium  is  a  rare  metal  which  occurs  naturally  with  alumin- 
ium as  a  silicate,  also  as  beryllium  silicate  (beryl),  colored  forms 
of  which  are  used  as  precious  stones.  Beryllium  forms  basic 
compounds  of  such  character  as  makes  it  suitable  for  use  in 
dental  cement. 

The  cement  powders  may  be  tested  for  beryllium  as  fol- 
lows: Fuse  a  little  of  the  powder  with  sodium  carbonate  (or 
the  double  sodium  potassium  carbonate);  dissolve  the  fused 
mass  in  dilute  hydrochloric  acid;  evaporate  to  dryness  and 
heat  to  120°  C.  to  dehydrate  the  silica;  take  up  in  water  with  a 
little  hydrochloric  acid  and  filter;  to  the  filtrate  (probably  con- 
taining Al,  Be,  Zn,  and  Ca)  add  a  little  ammonium  chloride, 
and  an  excess  of  ammonium  carbonate,  A1(0H)3,  Be(0H)2,  and 
CaCOs,  will  be  precipitated.  The  beryllium,  however,  is  easily 
soluble  in  the  excess  of  (NH4)2C03.  Warm  (not  boil)  and  allow  to 
stand  for  some  time  to  insure  complete  separation  of  aluminium. 

{Note.  —  A1(0H)3  is  much  less  soluble  in  solution  of  (NH4)2C03  than  in  either 
NH4OH  or  even  NH4OH  and  NH4CI.) 

Filter.  Boil  the  filtrate  for  a  long  time,  when  the  beryllium  and 
some  zinc  will  be  precipitated.  Filter  and  dissolve  precipitate 
off  paper  in  dilute  hydrochloric  acid.  To  the  filtrate  containing 
BeCl2  and  ZnCla  add  NH4CI  in  excess  and  NH4OH,  which  will 

*  Dental  Summary,  1915,  p.  56. 


I40  DENTAL  METALLURGY 

give  a  precipitate  of  Be(0H)2.  If  beryllium  and  zinc  only  are 
present,  the  separation  by  boiling  may  be  unnecessary. 

The  liquid  may  be  tested  for  dissolved  phosphates  by  dilut- 
ing with  water  and  adding  armnonia  till  alkaUne;  if  the  mixture 
remains  clear,  phosphates  of  alumina,  calcium,  or  zinc  are 
absent.  Care  should  be  used,  however,  in  the  addition  of  the 
ammonia,  as  an  excess  of  this  reagent  will  redissolve  phosphate 
of  zinc. 

If  the  ammonia  is  too  strong,  a  precipitate  of  ammonium 
phosphate  may  be  obtained,  but  this  may  be  easily  redissolved 
by  the  simple  addition  of  water. 

SiHcate  cements,  synthetic  cements,  and  synthetic  porcelain 
are  names  applied  to  later  preparations  containing  silica,  alu- 
minium, and  sometimes  magnesia  in  addition  to  usual  cement 
constituents.  Dr.  Ames  is  authority  for  the  statement  that 
beryllium  is  useful  chiefly  for  advertising  purposes. 

It  might  be  well  to  remember  in  this  connection  that  the 
natural  sources  (ores)  of  beryllium  available  in  Europe  are 
richer  in  beryllium  than  those  obtained  in  this  country. 

Dr.  E.  O.  Hile,  in  the  Dental  Digest  for  1913,  page  441,  says 
that  the  production  of  de  Trey's  synthetic  porcelain  is  based 
upon  a  study  of  the  setting  of  Portland  cement.  The  liquid  of 
this  porcelain  contains  a  smaller  proportion  of  acid  than  any 
cement  liquid. 


CHAPTER  XVI. 
RECOVERY   OF  RESIDUE. 

Gold.  —  The  gold  scrap  may  be  recovered  in  two  ways : 
first,  by  fusion  with  suitable  flux;  second,  by  dissolving  in  aqua 
regia  and  precipitation  of  the  metal.  In  the  first  method  it 
is  necessary  to  remove  mechanically  the  impurities  as  far  as  pos- 
sible, then  mix  the  fairly  clean  gold  waste  with  potassium  nitrate 
and  a  little  borax,  and  fuse  in  a  clay  crucible.  The  gold  will 
separate  as  a  button  at  the  bottom  of  the  thoroughly  fused  slag. 

In  the  second  method  the  scrap  gold  is  dissolved  in  aqua 
regia  and  the  resulting  solution  of  gold  chloride  is  precipitated 
with  ferrous  sulphate  or  oxalic  acid.  The  latter  precipitant,  al- 
though working  more  slowly  than  the  iron,  does  not  precipitate 
platinum,  hence  in  case  platinum  is  present  it  is  the  better  re- 
agent to  use.  The  precipitated  gold  is  next  filtered,  thoroughly 
washed,  and  fused  in  clay  crucible  under  borax  and  potassium 
nitrate. 

Silver.  —  The  recovery  of  silver  is  best  accomplished  by 
dissolving  the  scrap  or  waste  in  nitric  acid  and  precipitating  as 
chloride,  then  reducing  the  chloride  to  metallic  silver  either  by 
treatment  with  pure  zinc  or  by  fusion  with  sodium  carbonate. 
If  tin  is  present  in  the  scrap,  the  nitric  acid  will  form  metastannic 
acid,  a  white  insoluble  powder  rather  difficult  to  filter.  Hence, 
it  is  better  to  wash'  this  by  decantation  several  times  with  dis- 
tilled water,  which  will  remove  practically  all  the  silver.  From 
the  nitric-acid-  solution  the  silver  may  be  precipitated  by  salt  or 
hydrochloric  acid.  This  precipitate  must  be  washed  till  the 
wash-water  is  practically  free  from  chlorine,  then  dried  and  fused 

141 


142  DENTAL  METALLURGY 

with  sodium  carbonate,  when  a  button  of  pure  silver  will  be  ob- 
tained. 

If  preferred,  the  precipitated  chloride  of  silver  may  be  washed 
once  by  decantation,  then  agitated  with  pure  zinc,  when  the 
following  reaction  takes  place : 

2  AgCl  +  Zn  =  ZnClo  +  2  Ag. 

The  finely-di\'ided  silver  (in  the  form  of  nearly  black  powder) 
must  be  washed  free  from  chlorine,  carefully  dried  and  fused 
under  carbonate  of  sodium,  or,  after  drjing,  it  may  be  weighed 
and  dissolved  at  once  if  a  solution  is  desired.  If  the  silver  residue 
contains  mercury  this  may  be  driven  off  by  heat  before  solution 
is  attempted. 

Mercury.  —  ^Mercury  which  has  been  used  in  making  amal- 
gams is  best  purified  by  distillation.  Mercury  which  needs 
simply  to  be  freed  from  dirt,  dust,  or  sHght  traces  of  other 
metals  may  be  purified  as  follows:  If  a  piece  of  filter-paper  is 
fitted  closely  in  a  glass  funnel,  a  pin-hole  made  in  the  joint 
and  the  paper  thoroughly  wetted  with  water  and  the  mercury  to 
be  purified  placed  on  the  paper,  the  hea\y  metal  will  run  through 
the  pin-hole,  leaxing  practically  aU  the  dirt  clinging  to  the  wet 
filter-paper.  Such  mercury  may  also  be  cleansed  by  filtering 
through  chamois-skin. 

In  case  the  mercury  contains  slight  amounts  of  other  metals, 
if  it  is  digested  wAih.  a  very  dilute  nitric  acid,  the  acid  wiU  gen- 
erally first  dissolve  the  impurities  and  afterwards  a  little  of  the 
mercury-  itself.  Then  thorough  washing  with  water  mil  remove 
all  excess  of  acid  and  all  soluble  salts  which  may  have  been 
formed.  Pure  mercury  should  have  no  coating  of  any  sort  on 
its  surface,  and  if  a  few  globules  are  allowed  to  run  down  a 
smooth  inclined  plane,  they  should  leave  no  "  tail  "  behind. 


PART    III. 
VOLUMETRIC   ANALYSIS. 

CHAPTER  XVII. 
STANDARD    SOLUTIONS. 

Volumetric  analysis  is  the  determination  of  the  quantity 
of  a  particular  substance  contained  in  a  given  sample  by  means 
of  volumetric  or  standard  solutions.  By  means  of  standard 
solutions,  it  is  possible  to  determine  easily  and  quickly  the 
strength  of  a  peroxide  of  hydrogen  solution,  the  percentage  of 
silver  in  an  amalgam  alloy,  or  the  amount  of  gold  in  a  plate 
or  solder,  and  it  is  volumetric  analysis  thus  specialized  and 
adapted  to  dental  purposes  that  we  shall  consider. 

The  standard  solution  may  be  so  prepared  that  it  has  an 
arbitrary  or  special  value,  such,  for  instance,  as  the  silver-nitrate 
solution  usually  used  in  determining  the  amount  of  chlorine 
in  urine,  i  c.c.  of  this  solution  being  equal  to  ten  milligrams  of 
salt  (NaCl) ;  or  its  standardization  may  be  made  with  reference 
to  the  molecular  weights  of  the  reagents  employed,  so  that  solu- 
tions of  a  similar  nature  will  be  of  equivalent  values. 

Normal  and  decinormal  solutions,  or  the  volumetric  solutions 
of  the  U.  S.  P.,  are  of  this  character. 

A  normal  solution  may  be  defined  as  one  containing  the 
hydrogen  equivalent  of  the  reagent  in  grams  per  Uter.  This 
definition  may  be  explained  by.  saying  that  the  solution  contains 
the  molecular  weight  of  the  reagent  in  grams  per  Kter  provided 
the  reagent  is  of  univalent  basicity;  otherwise  such  part  of  the 
molecular  weight  is  taken  as  shall  represent  the  molecule  reduced 
to  a  univalent  basicity. 

143 


144  VOLUMETRIC  ANALYSIS 

For  example,  a  normal  (N/i)  solution  of  hydrochloric  acid 
or  of  potassium  hydroxide  would  contain  the  molecular  weight 
per  liter;  one  of  sulphuric  acid  or  of  calcium  hydrate  would 
contain  one-half  the  molecular  weight  per  liter. 

If  the  process  involves  oxidation,  the  oxidizing  power  of  the 
reagent  relative  to  one  atom  of  hydrogen  determines  the  pro- 
portion of  the  molecular  weight  to  use ;  for  example :  iodine  (I2) 
and  hydrogen  peroxide  (H2O2)  will  each  require  half  the  molec- 
ular weight  per  liter  to  make  a  normal  solution  because  in  each 
case  the  molecule  will  "  oxidize  "  two  atoms  of  hydrogen.  So 
K2Mn208,  which  will  furnish  five  atoms  of  available  oxygen 
capable  of  oxidizing  ten  atoms  of  hydrogen,  requires  only  one- 
tenth  of  its  molecular  weight  in  1000  c.c.  to  produce  a  normal 
solution. 

It  will  be  seen  from  the  above  explanation  that  equal  volumes 
of  normal  solution  will  always  bring  about  exact  reactions. 

The  normal  solution  should  not  be  confused  with  molar 
(M/i)  solution  used  elsewhere  in  the  book,  which  contains  the 
molecular  weight  of  the  reagent  in  grams  per  liter  without  regard 
to  the  hydrogen  equivalent;  for  example:  a  molar  solution  of 
H2SO4  contains  ninety-eight  grams,  while  a  normal  solution 
contains  forty-nine  grams  per  liter. 

Exact  reactions  between  molar  solutions  are  produced  when 
volumes  corresponding  to  the  respective  number  of  molecules 
taking  part  in  the  reaction  are  used.     See  Exp.  16,  page  371. 

The  normal  factor  is  the  weight  of  reagent  contained  in  one 
cubic  centimeter  of  the  normal  solution. 

The  volumetric  process  and  the  use  of  the  normal  factor 
will  be  most  clearly  understood  by  the  explanation  of  a  specific 
example. 

We  will  suppose  that  we  have  prepared  a  normal  solution  of 
NaOH  and  wish  to  ascertain  the  strength  of  a  sample  of  dilute 
HCl.  The  normal  solution  will  contain  the  molecular  weight 
in  grams  of  NaOH  per  liter  or  forty  grams  absolute  NaOH. 


STANDARD  SOLUTIONS  '145 

The  molecular  weight  of  HCl  being  36.4  (36.37),  a  normal 
solution  of  HCl  will  contain  36.4  grams  absolute  HCl;  and,  if 
a  Hter  of  normal  NaOH  were  added  to  a  Uter  of  normal  HCl, 
exact  neutralization  would  result: 

NaOH  +  HCl  =  NaCl  +  HoO. 
40         36.4       58.4  18 

The  one  liter  of  normal  alkali  (containing  40  grams  NaOH) 
is  exactly  neutralized  by  36.4  grams  of  HCl,  or  i  c.c.  of  normal 
alkali  by  0.0364  gram  of  HCl.  0.0364  is  normal  factor  of 
HCl. 

Now,  if  by  our  process  of  analysis  we  find  that  it  takes  just 
21  c.c.  of  the  NaOH  solution  to  exactly  neutralize  10  c.c.  of 
HCl  solution,  i  c.c.  of  NaOH  being  equal  to  0.0364  gram  HCl, 
21  c.c.  of  NaOH  will  be  equal  to  0.0364  x  21,  or  0.7644  gram 
HCl,  or  10  c.c.  of  the  HCl  solution  contains  0.7644  gram  of 
absolute  HCl,  equivalent,  approximately,  to  7.64%. 

It  has  becoine  apparent  that  in  carrying  out  .this  process 
three  things  are  absolutely  necessary: 

1.  Methods  for  the  preparation  of  standard  solutions. 

2.  Apparatus  for  accurate  measurements  of  both  the  standard 
solution  and  the  unknown. 

3.  Means  for  determining  just  when  the  point  of  exact 
neutralization  is  reached.  This  point  is  known  as  the  "  end 
point  "  and  is  shown  by  "  indicators  "  of  various  kinds. 

Preparation  of  Standard  Solutions.  —  Experience  has  shown 
that  normal  solutions  are  in  many  cases  less  convenient  to  work 
with  than  those  much  more  dilute,  both  on  account  of  the  keep- 
ing quaHties  of  th^  standard  solution  and  the  accuracy  of  manip- 
ulation; and,  for  the  purposes  oi  dental  chemistry,  a  decinormal 
or  one-tenth  normal  solution  represented  by  N/io  will  generally 
be  used. 

In  working  with  an  N/io  solution,  the  factor  used  in  cal- 
culations of  results  will  be  one-tenth  of  the  normal  factor  and 


146  VOLUMETRIC  ANALYSIS 

is  termed  an  N/io  factor.  Other  fractional  proportions  of  the 
normal  solution  may  be  used  as  the  centinormal,  N/ioo,  or 
seminormal,  X/2.  While  the  decinormal  solution  contains 
one-tenth  of  the  hydrogen  equivalent  of  reagent  in  grams  per 
liter,  and  this  amount  is  very  easy  to  calculate,  it  is  often  very 
difficult  to  weigh  out  the  exact  amount  required.  For  instance, 
we  want  an  N/io  solution  of  HCl.  HCl  is  a  gas  soluble  in 
water  and  the  strengths  of  the  solutions  vary  greatly,  so  we  can- 
not weigh  out  3.637  grams  of  absolute  HCl  to  put  in  1000  c.c.  of 
water  though  we  know  this  is  just  the  amount  necessary  to 
produce  our  N/io  solution.  Thus,  one  of  the  first  practical 
difficulties  in  making  up  standard  solutions  is  to  find  some  sub- 
stance which  can  be  weighed  accurately  and  the  exact  chemi- 
cal composition  of  which  may  be  rehed  upon. 

Crystallized  oxalic  acid  is  such  a  compound,  although  care' 
must  be  taken  that  the  crystals  are  dry  and  yet  contain  all 
their  water  of  crystalhzation;  in  other  words,  are  actually 
represented  by  the  formula  H2C204,2  H2O.  Fused  carbonate  of 
sodium  is  another  such  compound.  If  the  purest  obtainable 
bicarbonate  of  soda  is  fused  till  no  further  change  takes  place, 
cooled,  and  powdered,  the  product  is  pure  enough  for  the  prep- 
aration of  a  standard  solution  for  ordinary  use. 

For  the  preparation  of  volumetric  solutions  it  is  necessary  to 
have  a  balance  which  wiU  weigh  accurately  to  at  least  two 
decimal  points.  It  will  be  much  better  to  have  a  balance  sen- 
sitive to  one  milligram.  Balances  of  this  sort  inclosed  in  a  glass 
case  can  be  obtained  at  a  very  reasonable  price.  Fig.  12  on 
page  147  represents  such  a  balance. 

It  is  also  essential  to  have  flasks  capable  of  holding  100,  250, 
500,  and  1000  c.c.  carefully  graduated  on  the  neck,  represented 
in  Fig.  13,  page  147. 

Graduated  cyHnders  (Fig.  14)  are  not  so  well  suited  for  the 
preparation  of  standard  solutions,  as  the  greater  breadth  of  the 
column  of  Hquid  makes  accurate  reading  much  more  difficult. 


STANDARD  SOLUTIONS 


-147 


Fig.  12. 


Fig.  13. 


Fig.  14. 


Fig.  15. 


Fig.  16. 


148  VOLUMETRIC  ANALYSIS 

Small  cylinders  of  100  c.c.  or  less  are  useful  in  making  up 
odd  amounts  of  solution. 

In  the  process  of  analysis  it  will  be  necessary  to  have  pipettes 
(Fig.  15)  measuring  5  and  10  c.c,  also  a  burette  (Fig.  16),  from 
which  the  standard  solution  may  be  used.  The  burettes  may 
be  had  in  a  variety  of  styles  and  sizes,  a  very  serviceable  one 
being  of  25  c.c.  capacity  and  graduated  in  tenths  of  a  cubic  centi- 
meter. It  may  have  a  glass  stop-cock  or  it  may  be  furnished 
with  a  glass  tip  with  rubber  connector  and  pinch-cock. 

A  set  of  measuring-instruments  which  have  been  carefully 
compared  with  one  another  should  be  kept;  that  is,  the  looo-c.c. 
flask  should  be  exactly  filled  by  taking  the  loo-c.c.  flask  full  to 
the  mark  just  ten  times,  thus  enabling  one  accurately  to  take 
aliquot  parts  of  any  given  solution. 

Indicators. 

The  third  requisite  for  carrying  out  a  volumetric  process 
is  a  method  for  determining  the  end  point  of  the  reaction;  that 
is,  we  must  know  when  there  has  been  a  suflicient  quantity 
of  a  standard  solution  added  to  an  unknown  solution.  Phenol- 
phthalein  gives  a  red  color  with  alkahs,  which  is  discharged 
by  the  addition  of  acid  till  the  solution  becomes  colorless  as  it 
becomes  neutral  or  acid.  Litmus  gives  a  blue  color  with  al- 
kalis and  a  red  with  acids;  Methyl  orange  can  be  used  with 
carbonates  and  mineral  acids;  it  does  not  work  so  well  with 
organic  acids.  The  color  is  pink  in  acid  and  yellow  in  alka- 
line solution.  Lacmoid  is  useful  in  cases  where  the  acid  prop- 
erties of  such  salts  as  alum  or  zinc  chloride  might  interfere  with 
the  use  of  Htmus  or  phenolphthalein.  The  different  indicators 
do  not  all  change  color  at  exactly  the  same  point  in  the  process 
of  neutralization,  and  it  is  possible  for  a  solution  to  be  alkaline 
to  Htmus  and  acid  to  phenolphthalein  at  the  same  time.  Hence 
uniformity  in  the  use  of  indicators  is  desirable.     In  physiological 


STANDARD  SOLUTIONS  149 

chemistry,  congo  red,  tropasolin  00,  and  dimethylaminoazoben- 
zene  are  also  used. 

The  end  point  may  be  indicated  by  excess  of  a  standard 
solution  if  it  happens  to  be  highly  colored,  as  potassium  per- 
manganate. Thin  starch  paste  is  used  as  an  indicator  in  oper- 
ations involving  the  use  or  liberation  of  free  iodine.  Other 
indicators  will  be  considered  as  we  have  occasion  to  use  them  in 
the  various  analytical  processes. 

The  processes  of  volumetric  analysis  may  be  divided  into 
three  classes:  First,  acidimetry  and  alkalimetry.  Second,  oxi- 
dation and  reduction.     Third,  precipitation. 


Acidimetry  and  Alkalimetry. 

Acidimetry  and  alkalimetry  includes  all  standardized  solu- 
tions, either  acid  or  alkahne,  which  may  be  used  in  neutralizing 
solutions  of  unknown  strength  of  an  opposite  character.  For 
instance,  the  strength  of  vinegar  is  determined  by  neutralizing 
a  known  volume  with  standard  alkali. 

For  present  purposes  two  standard  acids  and  one  standard 
alkahne  solution  will  be  sufficient. 


DECINORMAL   OXALIC   ACID. 

The  first  of  these  may  be  decinormal  oxaHc  solution  prepared 
from  recently  recrystalHzed  and  carefully  dried  acid.  The 
composition  of  these  crystals  should  be  H2C2O4.2  H2O,  having 
molecular  weight  of  126. 

If  we  consider  the  reaction  involved  in  the  neutralization 
of  oxahc  acid  (H2C2O4  +  2  NaOH  =  Na2C204  -(-  2  H2O)  we  see 
that  twice  as  much  alkah  is  required  as  would  be  necessary  to 
neutralize  a  monobasic  acid  like  HCl.  Hence  to  obtain  our 
hydrogen  equivalent  we  divide  the  molecular  weight  of  oxalic 
acid  by  two,  which  will  give  us  a  weight  in  grams  to  be  dis- 


I50  VOLUMETRIC  ANALYSIS 

solved  in  sufficient  water  to  make  one  liter  of  normal  solution. 
A  decinormal  solution  will  be  one-tenth  of  this  strength. 

For  class  use,  each  student  may  prepare  500  c.c.  of  this 
solution  by  dissolving  3.15  grams  of  pure  crystallized  oxalic 
acid  in  water  and  dilute  to  a  half-liter.  The  graduated  flasks 
are  usually  constructed  to  be  used  at  a  temperature  of  60°  F. 
or  15°  C.  and  for  accurate  work  solutions  must  be  brought 
to  this  temperature.  After  the  oxaHc  acid  solution  has  been 
prepared  the  decinormal  alkali  may  be  made  as  follows: 

DECINORMAL   SODIUM  HYDROXIDE. 

Weigh  out  carefully  two  and  a  half  grams  of  caustic  soda  or 
three  grams  of  caustic  potash  and  dissolve  in  less  than  500  c.c.  of 
distilled  water.  After  the  solution  has  thoroughly  cooled,  fill  a 
burette  with  it.  Place  10  c.c.  of  standard  acid  previously 
prepared  in  a  white  porcelain  dish  of  about  250  c.c.  capacity, 
add  20  c.c.  distilled  water  and  two  or  three  drops  of  phenol- 
phthalein  (2%  phenolphthalein  in  alcohol  and  water,  equal  parts) ; 
then  carefully  run  in  from  the  burette,  with  constant  stirring, 
the  alkali  solution  until  a  permanent  pink  tint  is  produced. 
This  process  is  known  as  "  titration,"  and  will  hereafter  be  so 
designated. 

The  work  will  be  more  satisfactory  if  the  titration  is  made 
for  the  appearance  of  color  rather  than  the  disappearance  of 
color,  as  would  have  been  the  case  had  the  standard  acid  run 
into  the  measured  alkali  solution. 

The  Calculation.  —  Supposing  it  has  taken  8.2  c.c.  of  the 
alkali  to  exactly  neutralize  the  10  c.c.  of  N/io  acid,  it  follows  that 
in  the  8.2  c.c.  there  is  sufficient  alkali  to  equal  or  to  make  10  c.c. 
of  an  N/io  alkali  solution;  hence  we  may  add  1.8  c.c.  of 
distilled  water  to  every  8.2  c.c.  of  alkali  solution,  thereby 
reducing  it  to  decinormal  strength.  Practically  we  should  take 
410  c.c.  of  alkali  solution  and  in  a  graduated  flask  make  it  up  to 
500  c.c.  with  distilled  water.     It  will  be  necessary  to  make 


STANDARD  SOLUTIONS  151 

several    titrations  and  average  the  results  before  making  the 
calculation. 

From  the  standard  alkali  N/io  solutions  of  HCl  or  H2SO4 
may  be  prepared  in  a  similar  manner,  it  being  impossible  to 
accurately  weigh  either  of  these  two  acids.  In  titrating  a  car- 
bonate, if  an  indicator,  such  as  phenolphthalein,  which  is  sensi- 
tive to  carbonic  acid,  is  used,  it  is  necessary  to  keep  the  solution 
at  a  boiling  temperature  or  at  least  bring  it  to  a  boil  after  every 
addition  from  the  burette. 

VOLUMETRIC  DETERMINATION   OF  ACETIC  ACID. 

As  an  example  of  acidimetry  and  alkalimetry  determine  the 
strength  of  a  sample  of  \-inegar  as  follows: 

Measure  accurately  into  a  white  porcelain  dish  of  150-250 
c.c.  capacity  i  c.c.  of  the  sample.  This  may  be  measured  either 
with  a  carefully  graduated  i-c.c.  pipette  or  more  accurately 
by  diluting  10  c.c.  of  the  sample  to  100  c.c.  in  a  graduated  flask, 
then  using  10  c.c.  of  the  dilution  for  the  titration,  the  titration 
to  be  performed  with  N/io  NaOH,  using  phenolphthalein  as  an 
indicator. 

The  molecular  weight  of  acetic  acid  is,  in  round  numbers, 
60;  hence  the  N/io  factor  of  acetic  acid  will  be  0.006  (acetic  acid 
being  monobasic,  HC2H3O2).  To  ascertain  the  strength  of  the 
sample  of  vinegar  it  is  necessary  to  multiply  the  number  of 
cubic  centimeters  used  by  this  factor,  0.006,  which  will  give 
the  amount  of  absolute  acid  calculated  as  acetic  in  i  c.c.  (prac- 
tically I  gram)  of  the  sample.  Thus,  if  8  c.c.  of  N/io  alkali 
were  required  to  neutralize  i  c.c.  of  vinegar,  multiplying  the 
factor  0.006  by  8  would  give  0.048  gram  of  absolute  acetic  add 
in  I  c.c.  of  vinegar,  which  is- equivalent  to  4.8%. 

VOLUMETRIC   SOLUTION   OP  HYDROCHLORIC  ACLD. 

The  volatile  character  of  hydrochloric  acid  renders  a  solution 
of  normal  strength  rather  unstable,  so  decinormal  or  weaker 


152  VOLUMETRIC   ANALYSIS 

solutions  of  this  acid  are  commonly  employed.  Take  a  solution 
of  hydrochloric  acid  which  shall  contain  four  to  four  and  one-half 
grams  per  liter.  Make  several  titrations  with  decinormal  so- 
dium hydroxide  and  from  the  average  of  these  dilute  to  decinor- 
mal strength  as  follows:  the  acid  solution  has  been  made  rather 
•stronger  than  decinormal  so  the  lo  c.c.  of  dilute  HCl  may  have 
required  12.5  c.c.  of  standard  alkali  for  exact  neutralization.  In 
this  case  add  250  c.c.  of  distilled  water  to  1000  c.c.  of  the  acid. 

DETERMINATION    OF   MAGNESIUM  HYDRATE    OR   MILK 
OF   MAGNESIA. 

The  strength  of  milk  of  magnesia  may  be  volumetrically 
determined  as  follows:  To  five  grams  of  carefully  mixed  and 
accurately  weighed  milk  of  magnesia  add  twenty-five  cubic 
centimeters  of  normal  sulphuric  acid.  When  dissolved,  dilute 
the  solution  to  250  c.c.  Mix  thoroughly  and  titrate  25  c.c. 
of  this  solution  with  decinormal  alkali.  The  result  of  this 
titration  multiplied  by  ten  will  give  the  uncombined  acid. 
Subtract  this  from  the  volume  of  standard  acid  originally  used 
and  calculate  the  amount  of  Mg(0H)2.  Each  cubic  centimeter 
of  the  normal  acid  corresponds  to  0.02917  gram  of  magnesium 
hydroxide. 

Note.  —  This  process  is  based  upon  the  last  revision  of  the  United  States 
Pharmacopoeia  in  which  the  term  cubic  centimeter  is  everywhere  replaced  by  the 
name  mils.  This  term  indicates  a  miUiliter  or  one-thousandth  of  a  liter,  which  the 
revisers  consider  to  be  more  accurate  than  cubic  centimeter. 

CARBONATE    TITRATION. 

While  perhaps  phenolphthalein  is  the  most  serviceable  of  all 
indicators  in  common  use,  it  is  so  sensitive  to  carbon  dioxide  that 
any  titration  which  results  in  the  liberation  of  CO2  must  be 
modified  by  boiling  the  solution  thoroughly  after  each  addition 
of  acid.  This  makes  the  operation  somewhat  tedious,  but  it  is 
to  be  preferred  to  the  use  of  other  and  less  sensitive  indicators 
which  may  not  be  affected  by  the  carbon  dioxide. 


standard  solutions  153 

Analysis  by  Oxidation  and  Reduction, 
decinormal  permanganate  of  potassium. 

If  to  a  hot  solution  of  oxalic  acid  containing  sulphuric  acid, 
permanganate  of  potash  be  added,  the  following  reaction  takes 
place: 

2  KMn04  +  5  H0C.2O4  +  3  H0SO4  =  K0SO4  +  2  MnS04 
+  10  CO2  +  8  H2O. 

This  reaction  represents  a  very  valuable  method  of  volumetric 
analysis;  but,  inasmuch  as  it  is  not  a  process  of  neutralization, 
it  cannot  properly  come  under  the  head  of  acidimetry  and  alka- 
limetry, but  rather  under  a  distinct  classification,  the  determina- 
tion involving  oxidation  and  reduction. 

Standard  Permanganate  Solution.  —  In  the  reaction  given 
above  we  may  consider  that,  as  the  molecule  of  K2Mn208  breaks 
up,  three  of  the  eight  atoms  of  oxygen  are  required  to  form  the 
basic  oxides  K2O  and  2  MnO  (soluble  in  the  acid  as  K2SO4  and 
2  MnS04),  while  the  remaining  five  atoms  are  liberated  and 
constitute  the  active  chemical  agent  whereby  the  oxalic  acid  is 
oxidized  to  CO2  and  H2O.  Hence,  to  reduce  this  double  molec- 
ular weight  (316)  to  the  hydrogen  equivalent  necessary  for  a 
normal  solution,  it  is  divided  by  10  (five  atoms  of  oxygen  having 
a  valence  of  10). 

The  Decinormal  Solution  may  be  made  by  dissolving  3.16 
grams  of  pure  recrystallized  and  thoroughly  dried  crystals,  if 
they  can  be  obtained,  in  distilled  water,  and  making  the  solu- 
tion up  to  1000  c.c,  or  it  may  be  standardized  by  titration  with 
the  N/io  oxalic  acid  previously  prepared;  in  this  case  one  would 
proceed  as  follows : 

Make  a  solution  slightly  stronger  than  the  standard  required, 
say  about  3.5  grams  of  the  ordinary  pure  crystals  in  a  liter  of 
water;  with  this  fill  a  burette,  place  10  c.c.  of  N/io  oxaHc  acid 
measured  from  a  pipette  in  an  evaporating-dish  or  casserole, 
dilute  with  about  50  c.c.  of  water,  add  about  10  c.c.  of  dilute 


154  VOLUMETRIC  ANALYSIS 

sulphuric  acid,  and  heat  the  mixture  nearly  to  the  boiling-point. 
Then  titrate  with  the  permanganate  from  the  burette.  The 
permanganate  will  at  first  be  rapidly  decolorized,  but  as  the 
operation  progresses  the  color  fades  more  slowly  till  at  last  a 
faint  permanent  pink  color  indicates  that  the  "  end  point  "  has 
been  reached. 

The  temperature  must  be  kept  above  60°  C.  throughout  the 
titration  or  the  oxidation  will  take  place  too  slowly  and  an 
apparent  end  point  will  be  obtained  before  the  reaction  is  com- 
pleted. 

If  the  solution  turns  muddy  during  the  operation,  it  is  due 
to  an  insufficient  amount  of  sulphuric  acid  and  more  should 
be  added.  The  calculation  is  made  as  in  the  case  of  the  N/io 
NaOH  described  on  page  150.  The  standard  permanganate 
should  be  preserved  in  full,  well-stoppered  bottles  and  kept  in  a 
dark  place. 

It  is  better  to  have  the  KMn04  solution  made  up  a  day  or 
two  before  it  is  standardized,  thereby  allowing  for  oxidation  of 
traces  of  ammonia,  etc.,  which  the  water  may  contain. 

DETERMINATION  OF  PEROXIDE  OF  HYDROGEN. 

In  determining  the  strength  of  peroxide  use  i  c.c.  of  the 
sample  measured,  as  in  the  case  of  vinegar  (which  see),  dilute 
with  50  c.c.  of  distilled  water,  add  10  c.c.  of  dilute  sulphuric 
acid,  and  titrate  with  the  permanganate  in  exactly  the  same 
manner  as  detailed  in  the  preceding  paragraph,  with  the  excep- 
tion that  the  titration  must  be  made  cold.  The  reaction  takes 
place  so  easily  that  heat  is  unnecessary  and  even  a  slight  elevation 
of  temperature  may  result  in  loss  of  hydrogen  peroxide,  the  reac- 
tion in  this  case  being  as  follows: 

2  KMn04  +  5  H2O2  +  3  H2SO4  =  K0SO4  +  2  MnS04  +  5  O2 
+  8  H2O. 

The  aqueous  solutions  of  peroxide  on  the  market  used  as 


STANDARD  SOLUTIONS  155 

antiseptics  contain  about  3%  absolute  H2O2  and  yield  approxi- 
mately ten  volumes  of  available  oxygen;  that  is,  10  c.c.  of  solu- 
tion will  yield  100  c.c.  of  oxygen.  The  calculation  may  be 
made  to  express  strength  of  the  peroxide  in  terms  of  percentage 
of  absolute  H0O2  by  multiplying  the  number  of  cubic  centimeters 
of  N/io  KMn04  decolorized  by  i  c.c.  of  solution  by  0.17,  or  to 
express  the  strength  in  volumes  of  available  oxygen  by  multiply- 
ing the  number  of  cubic  centimeters  of  solution  by  0.56  (more 
accurately  0.55  94) . 

DECINORMAL   IODINE 

A  decinormal  solution  of  iodine  may  be  prepared  by  dissolv- 
ing 12.68  grams  of  pure  iodine  crystals  in  one  hter  of  water 
by  the  aid  of  about  18  grams  of  pure  potassium  iodide. 

Iodine  of  sufficient  purity  may  be  obtained  by  carefully  re- 
subliming  selected  and  carefully  dried  crystals  of  so-called 
"  chemically-pure  "  iodine. 

DECmORMAL   SODIUM  THIOSULPHATE. 

Na2S203.5  HoO,  molecular  weight  =  248.24.  This  solution 
may  be  made  by  weighing  directly  24.824  grams  of  the  pure 
crystallized  salt,  dissolving  in  water  and  diluting  to  1000  c.c,  or 
it  may  be  standardized  by  titration  with  a  decinormal  iodine 
solution,  the  reaction  being  as  follows: 

2  Na2S203  -f-  2  I  =  2  NaU-  NasSiOe. 

The  indicator  used  is  a  very  dilute  starch  paste,  which  gives 
the  characteristic  blue  color  as  soon  as  free  iodine  is  in  excess. 

By  means  of  these  two  standard  solutions  (iodine  and  sodium 
thiosulphate)  a  variety  of  determinations  may  be  made  with 
great  accuracy.  Any  substance  which  will  'liberate  iodine  from 
potassium  iodide  may  be  quantitated  by  adding  an  excess  of 
the  potassium  salt  and  titrating  the  free  iodine  with  thiosulphate 
solution,  using  starch  paste  as  usual  for  an  indicator. 

Peroxide  of  hydrogen  may  be  thus  determined  as  easily  as 


156  VOLUMETRIC  ANALYSIS 

by  the  permanganate  method  previously  given.  The  process, 
being  that  of  Kingzett,  is  given  as  follows  by  Sutton: 

Mix  10  c.c.  of  peroxide  solution  to  be  examined  with  about 
31  c.c.  of  dilute  sulphuric  acid  (1-2)  in  a  beaker,  adding  crystals 
of  potassium  iodide  in  suflEicient  quantity,  and  after  standing 
five  minutes  titrating  the  liberated  iodine  with  N/io  thiosul- 
phate  and  starch.  The  peroxide  solution  should  not  exceed  the 
strength  of  two  volumes;  if  stronger,  it  must  be  diluted  pro- 
portionately before  the  analysis. 

In  the  case  of  a  very  weak  solution  it  will  be  advisable  to 
titrate  with  N/ioo  thiosulphate. 

I  c.c.  N/io  thiosulphate  =  0.0017  gram  H2O2. 

DETERMINATION   OF   IODINE   SOLUTION. 

Titrate  10  c.c.  of  the  iodine  solution  with  standard  sodium 
thiosulphate  until  the  iodine  color  has  become  a  pale  yellow; 
then,  and  not  until  then,  add  the  starch  paste  indicator  and  con- 
tinue titration  until  blue  color  is  discharged. 

DETERMINATION   OF  HYPOCHLORITE   SOLUTION. 

By  the  use  of  sodium  thiosulphate  the  strength  of  chlorinated 
lime,  used  as  a  disinfectant,  may  be  easily  determined.  The 
following  process  is  based  upon  the  assay  given  in  the  nine- 
teenth revision  of  the  Pharmacopoeia  (19 16). 

Into  a  small,  tared,  stoppered,  weighing  bottle  containing 
10  c.c.  of  distilled  water  introduce  about  two  grams  of  chlo- 
rinated lime  and  weigh  carefully.  In  a  small  mortar  rub  this 
mixture  with  repeated  portions. of  water  which  are  to  be  carefully 
transferred  to  a  500-c.c.  graduated  cylinder.  WTien  one  or  two 
hundred  c.c.  of  water  have  been  used  in  this  way  rinse  the 
weighing  flask  and  mortar  several  times  with  distilled  water, 
adding  the  rinsings  to  the  graduated  cylinder,  and  finally  making 
the  entire  volume  measure  exactly  500  c.c.     Mix  thoroughly 


STANDARD  SOLUTIONS  157 

and  allow  to  settle.  Take  twenty-five  to  fifty  c.c.  of  this  mix- 
ture accurately  measured,  transfer  to  a  porcelain  dish,  add  half  a 
gram  of  potassium  iodide  and  two  to  three  c.c.  of  acetic  acid  and 
titrate  with  decinormal  sodium  thiosulphate  solution,  using 
dilute  starch  solution  as  an  indicator.  Each  cubic  centimeter 
of  the  standard  thiosulphate  corresponds  to  0.003546  of  a  gram 
of  available  chlorine. 

Note.  —  The  strength  of  metallic  peroxides  may  be  determined  by  acting 
upon  the  peroxide  with  hydrochloric  acid,  conducting  the  liberated  chlorine  into 
a  potassium  iodide  solution  and  titrating  the  liberated  iodme  with  standard 
thiosulphate. 

VOLUMETRIC   DETERMINATION   OF   ARSENIC. 

Mohr's  method  of  oxidation  with  iodine  is  a  practical  one. 
The  titration  is  made  with  N/io  iodine  and  starch  as  usual, 
except  that  the  solution  should  be  at  first  neutral  and  then 
about  20  c.c.  of  saturated  solution  of  sodium  bicarbonate  should 
be  added  to  every  o.i  gram  of  AS2O3  supposed  to  be  in  the  un- 
known, thus  giving  a  certain  definite  alkalinity.  If  the  solution 
is  acid,  neutrahze  with  sodium  bicarbonate,  then  make  alkaline 
with  more  bicarbonate  as  above. 

VOLUMETRIC  DETERMINATION    OF   GOLD. 

While  gold  is  usually  determined  quantitatively  by  assay 
in  a  dry  way  (page  164)  it  may  be  determined  very  accurately 
by  titration  with  thiosulphate  solution.  Fatka  (Chem.  Zeit.) 
recommends  the  following  process  based  upon  the  fact  that 
a  neutral  solution  of  gold  salt  wdth  potassium  iodide  will  give 
a  greenish  precipitate.  When  an  excess  of  potassium  iodide 
is  used  no  precipitate  is  formed,  but  a  solution  of  Auls  as  AUKI4 
results.  This  is  of  a  brown  color  and  may  be  titrated  with 
N/io  thiosulphate  solution,  when  the  following  reaction  takes 
place : 

AUKI4  +  2  NaoSsOg  =  AUKI2  +  2  Nal  -f  Na2S406. 


158  VOLUMETRIC  ANALYSIS 

Process:  10  c.c.  of  gold  solution  containing  approximately 
2%  of  gold  is  treated  with  4  grams  of  potassium  iodide  diluted 
to  100  c.c.  with  water  and  titrated  with  N/io  Na^S^Oa  solu- 
tion, using  starch  as  an  indicator. 

VOLUMETRIC  DETERMINATION   OF   GOLD. 
(Second  Method.) 

In  the  analysis  of  dental  alloy,  gold  will  remain  undissolved 
by  HNO3  and  will  be  weighed  with  the  Sn02.  It  should  be  sep- 
arated and  its  weight  deducted  before  calculation  is  made  for 
tin.  This  may  be  done  by  dissolving  the  gold  in  dilute  aqua 
regia,  evaporating  the  solution  of  gold  chloride  to  dryness,  dis- 
solving residue  in  distilled  water  and  proceeding  according  to  fol- 
lowing method  from  Schimpf's  Manual  of  Volumetric  Analysis. 

The  gold  must  be  in  the  form  of  chloride  (AuClg). 

To  the  solution  of  gold  chloride  a  measured  excess  of  N/i 
oxalic  acid  solution  is  added  and  the  mLxture  set  aside  for  twenty- 
four  hours. 

The  solution  is  then  made  up  to  a  definite  volume  (say  300 
c.c).  Then,  by  means  of  a  pipette,  100  c.c.  are  removed,  and 
the  excess  of  oxalic  found  by  titrating  with  N/io  permanganate 
in  the  presence  of  sulphuric  acid.     The  reaction  is 

2  AUCI3  +  3  H2C2O4  =  2  Au  +  6  HCl  +  6  CO2. 

Each  cubic  centimeter  of  N/i  oxalic  acid  solution  =  0.06523 
gram  of  Au,  or  0.1004  gram  of  AuCla. 

Analysis  by  Preclpitation. 

Because  certain  elements  possess  a  selective  affinity  for 
other  elements  it  is  possible  to  determine  many  substances 
quantitatively  by  precipitation.  That  is,  if  silver  nitrate  is 
added  to  a  mixture  of  a  soluble  chloride  and  a  chromate,  the 
chlorine  will  combine  first  with  the  silver,  forming  AgCl,  to  the 
exclusion  of  the  chromate.     After  the  last  trace  of  chlorine  has 


STANDARD  SOLUTIONS  -     159 

been  so  combined,  the  silver  chromate  will  be  formed,  which 
is  a  salt  with  an  intense  red  color;  hence  it  is  possible  to 
determine  the  strength  of  solutions  of  soluble  chlorides  by  titra- 
tion with  standard  AgNOs,  using  potassium  chromate  as  an  in- 
dicator. This  process  is  used  in  analysis  of  drinking-water,  of 
saliva,  and  of  urine,  but  for  each  of  these  it  is  desirable  to  have 
solutions  of  special  strength. 

A   DECINORMAL   SILVER   SOLUTION 

may  be  made  by  dissolving  seventeen  grams  of  pure  crystalHzed 
AgNOs  in  a  Hter  of  distilled  water,  and  with  this  a 

DECINORMAL  SODIUM  CHLORIDE   SOLUTION 

may  be  prepared  as  follows: 

Weigh  out  six  grams  of  the  purest  salt  obtainable  and  dis- 
solve in  approximately  one  Kter  of  distilled  water.  With  a 
pipette  measure  10  c.c.  of  this  solution  into  a  white  porcelain 
dish,  dilute  to  about  20  c.c.  with  H2O,  add  two  to  five  drops  of 
neutral  potassium  chromate  (K2Cr04)  and  add  AgNOs  from  a 
burette  till  a  faint  pink  color  persists. 

The  calculation  and  dilution  is  made  exactly  as  described 
on  page  150  in  the  preparation  of  a  standard  NaOH  solution. 
The  silver  nitrate  solution  used  to  determine  chlorine  in  urine 
may  be  prepared  of  such  a  strength  that  i  c.c.  precipitates  just 
10  milligrams  of  sodium  chloride.  This  is  equivalent  to  0.006065 
gram  of  chlorine.  A  solution  of  this  strength  is  produced 
when  29.075  grams  of  pure,  fused  silver  nitrate  are  dissolved  in 
sufficient  distilled  water  to  measure  one  Hter  of  solution.  If 
chlorine  is  to  be  determined  in  drinking-water,  it  is  usually  nec- 
essary to  concentrate  the  water  to  at  least  one-fifth  its  bulk  and 
then  to  use  not  more  than  one  or  two  drops  of  neutral  chromate 
as  indicator.  The  standard  silver  nitrate  for  this  titration 
should  be  very  dilute.     A  convenient  solution  may  be  prepared 


l6o  VOLUMETRIC  ANALYSIS 

by  diluting  the  standard  AgNOa  for  urine  i  to  lo.  In  saliva 
the  sample  may  be  diluted  with  an  equal  volume  of  water  and 
titrated  the  same  as  in  the  case  of  drinking-water.  In  all  quan- 
titative processes  where  silver  chromate  is  used  to  determine  the 
end  point  the  solution  must  be  practically  neutral,  as  the  for- 
mation of  this  salt  is  prevented  by  either  acids  or  alkalis. 

DECINORMAL  POTASSIUM   SULPHO-CYANATE. 

This  solution  may  be  made  in  a  manner  similar  to  that  pre- 
viously described  for  the  preparation  of  standard  sodium  chlo- 
ride solution,  except  that  a  fairly  strong  solution  of  ferric  alum 
should  be  used  as  indicator  and  the  titrated  solution  should 
contain  moderate  excess  of  nitric  acid. 

DETERMINATION   OF   SILVER   BY   SODIUM   CHLORIDE   SOLUTION. 

The  strength  of  neutral  silver  solutions  may  be  determined 
by  the  use  of  decinormal  sodium  chloride  using  yellow  potassium 
chromate  as  an  indicator.  It  is  better  to  add  the  silver  solution 
from  the  burette  as  the  precipitate  of  silver  chromate  which 
would  be  formed  by  adding  the  indicator  to  the  silver  solution 
disintegrates  with  difficulty. 

DETERMINATION   OF   SILVER   BY   POTASSIUM   SULPHO-CYANATE 

SOLUTION. 

Silver  may  be  determined  volumetrically  in  nitric  acid 
solution  by  titration  with  standard  KCNS  solution,  using  ferric 
alum  as  an  indicator.  The  sulphocyanate  solution  must  be 
standardized  against  decinormal  AgNOs  as  follows:  Prepare  a 
solution  containing  not  less  than  lo  grams  of  chemically  pure 
KCNS  per  Hter.  Place  this  solution  in  the  burette  and  put  in 
the  porcelain  dish  lo  c.c.  of  decinormal  AgNOs  which  has  been 
strongly  acidified  with  nitric  acid  and  fifteen  or  twenty  drops  of 


STANDARD  SOLUTIONS  l6l 

a  solution  of  ferric  alum,  added  as  an  indicator.  The  end  point 
is  indicated  by  the  faint  red  color  of  ferric  sulphocyanate,  pro- 
duced by  the  tirst  excess  of  KCNS.  The  calculation  will  be  the 
same  as  previously  described  in  the  preparation  of  N/io  NaOH 

(page  150). 

DETERMINATION    OF    CHLORINE    IN    URINE. 

A  rough  determination  of  chlorine  may  be  made  by  titrating 
10  c.c.  of  urine  with  standard  silver  nitrate,  using  potassium 
chromate  as  an  indicator  (see  page  159).  An  accurate  deter- 
mination may  be  made  by  acidifying  10  c.c.  of  urine  with  nitric 
acid.  Add  20  c.c.  of  decinormal  silver  nitrate  solution  and 
titrate  the  excess  of  silver  nitrate  by  using  standard  KCNS  with 
ferric  alum  as  an  indicator.  (In  this  case  the  presence  of  a 
considerable  quantity  of  silver  chloride  makes  it  unnecessary, 
and  in  fact  impracticable,  to  use  the  silver  solution  in  the  bu- 
rette.) Subtract  the  number  of  c.c.  of  N/io  AgNOs  used  for 
this  titration  from  the  20  c.c.  at  first  added  and  the-  remainder 
represents  the  chlorine  content  of  the  urine. 

VOLUMETRIC  DETERMINATION   OF   COPPER. 

Into  a  solution  of  copper,  free  from  other  metals  of  Group  I 
or  II,  pass  HoS  gas.  Wash  the  resulting  copper  sulphide  thor- 
oughly with  HoS  water,  and  dissolve  in  dilute  nitric  acid;  then 
wash  the  paper  in  warm  water,  add  to  the  filtrate  (wash  water) 
sodium  carbonate  until  precipitate  formed  is  nearly  dissolved; 
then  add  i  c.c.  of  dilute  NH4OH.  Titrate,  to  complete  dis- 
appearance of  blue  color,  with  KCN  solution  previously  stand- 
ardized after  this  same  method  against  pure  copper  wire.  A 
Httle  practice  is  required  in  determining  the  end  point  to  give 
the  process  any  degree  of  accuracy.  An  excess  of  ammonia 
should  be  avoided,  as  it  interferes  with  the  accuracy  of  the  end 
point. 


1 62  VOLUMETRIC  ANALYSIS 

VOLUMETRIC    DETERMINATION    OF    ZINC. 

(For  use  in  analysis  of  amalgam  alloys.) 

The  solution  from  which  silver  and  copper  have  been  re- 
moved, together  with  all  wash-water,  may  be  concentrated; 
if  acid  in  reaction  it  should  be  evaporated  to  dryness,  and  the 
residue  dissolved  in  water;  then  add  a  fairly  strong  solution 
of  oxaUc  acid  and  an  equal  volume  of  strong  alcohol.  Allow 
to  stand  15  to  30  minutes,  filter,  and  wash  with  70%  alcohol  till 
oxahc  acid  is  removed,  dry  until  the  alcohol  has  disappeared, 
dissolve  in  dilute  sulphuric  acid,  and  titrate  the  solution  with 
N /lo  permanganate  and  calculate  the  zinc  from  the  amount 
of  oxalic  acid  found. 

This  method  is  usually  fully  as  satisfactory  as  the  gravi- 
metric determination  given  on  page  165. 

VOLUMETRIC   DETERMINATION    OF   CALCIUM. 
(For  use  in  saliva  analysis.) 

This  method  is  based  upon  that  recommended  by  Dr.  Percy 
R.  Howe,  Dental  Cosmos,  April,  191 2.  To  5  c.c.  of  sahva,  add 
as  much  more  distilled  water  and  a  slight  excess  of  oxalic  acid 
or  ammonium  oxalate  (5  c.c.  of  normal  solution  will  be  sufficient). 
Add  ammonium  water  to  alkaline  reaction,  heat  nearly  to  the 
boihng  point,  and  allow  to  stand  for  twenty  to  thirty  minutes. 
Filter  through  a  hardened  filter  paper  into  a  small  beaker  which 
is  allowed  to  stand  on  a  piece  of  black  glazed  paper.  Under 
these  circumstances,  a  sHght  rotary  motion  of  the  beaker  will 
show  if  any  of  the  white  precipitate  of  calcium  oxalate  is  passing 
through  the  paper. 

After  filtration  is  complete,  wash  five  times  in  hot  distilled 
water;  then  place  the  precipitate,  together  with  the  paper,  into 
a  small  beaker,  add  about  30  c.c.  of  dilute  sulphuric  acid,  and 
heat  nearly  to  the  boiling  point;  then  titrate  with  N/20  perman- 
ganate solution. 


STANDARD  SOLUTIONS  "      163 

GRAVIMETRIC   DETERMINATIONS. 

Gravimetric  determinations  are,  as  a  rule,  more  accurate 
than  volumetric;  but  they  require  greater  care  and  attention 
to  details,  making  them  less  satisfactory  in  the  hands  of  the 
beginner.  Some  determinations,  however,  on  account  of  difiEi- 
culties  in  obtaining  accurate  end  points  and  absolute  separations, 
are  really  easier  when  made  by  gravimetric  processes.  A  few 
of  these  will  be  given. 

GRAVIMETRIC  DETERMINATION   OF   TIN   AS   SnOo. 

Tin  may  be  separated  from  dental  alloys  in  the  absence  of 
gold  or  platinum  by  simply  dissolving  the  alloy  in  nitric  acid. 
Tin  will  remain  as  a  white  insoluble  metastannic  acid.  "  As 
stated  on  page  40  metastannic  acid,  upon  long  standing,  will 
change  to  somewhat  soluble  compounds,  hence  this  operation 
should  be  completed  with  reasonable  rapidity.  After  complete 
disintegration  of  the  alloy,  the  insoluble  tin  compound  may  be 
separated  by  filtration  through  asbestos  fiber,  contained  in  a 
Gooch  crucible.     The  method  of  procedure  is  as  follows: 

A  little  fine  asbestos  fiber,  washed  in  acid  and  held  in  sus- 
pension in  water,  is  placed  on  the  bottom  of  the  crucible.  The 
crucible  is  then  placed  in  the  top  of  a  filtering  flask  from  which 
the  air  is  exhausted  by  the  suction  pump.  This  packs  the 
asbestos  down  firmly  on  the  bottom  of  the  crucible  in  a  thin 
layer,  and  care  should  be  taken  that  the  quantity  of  asbestos 
used  is  such  that  water  will  pass  through  it  easily.  The  cruci- 
ble with  asbestos  is  next  dried,  ignited,  and  weighed.  Now 
transfer  the  precipitate  of  tin  oxide  (metastannic  acid)  to  the 
crucible,  taking  care  that  ilone  is  lost,  and  wash  thoroughly  six 
or  eight  times,  then  dry,  ignite  strongly,  and  weigh  again. 

If  the  ignited  residue,  weighed  as  tin  oxide,  does  not  contain 
gold  or  platinum,  the  weight  of  tin  may  be  obtained  by  multi- 
plying the  weight  of  the  ash  by  0.788. 


1 64  VOLUMETRIC  ANALYSIS 

GRAVIMETRIC  DETERMINATION   OF    SILVER. 

The  gravimetric  determination  of  silver  is  not  difficult,  and 
is  rather  more  accurate  than  the  volumetric  method.  The 
silver  is  obtained  in  the  form  of  silver  chloride.  This  is  separated 
by  filtration  through  an  ashless  paper,  and  dried.  Then  the 
dried  precipitate  is  removed  as  completely  as  possible  onto  a 
square  of  black  glazed  paper  and  preserved  under  a  funnel  or 
bell  glass.  The  filter  paper,  containing  traces  of  silver  chlo- 
ride which  could  not  be  removed,  is  next  incinerated  in  a  pre- 
viously weighed  porcelain  crucible. 

As  slight  reduction  of  silver  chloride  to  silver  may  take  place 
during  the  ignition  of  the  paper,  it  is  necessary  to  add,  after  the 
paper  is  completely  burned,  a  drop  or  two  of  nitric  acid,  and  after 
the  excess  has  been  driven  off  by  gentle  heat,  a  drop  or  two  of 
hydrochloric  acid.  This  treatment  dissolves  any  reduced  silver 
and  precipitates  silver  chloride.  After  carefully  heating  to  dry 
the  precipitate  in  the  crucible,  the  reserved  portion  of  silver 
chloride  is  carefully  brushed  into  the  crucible,  and  the  whole 
ignited  until  the  silver  chloride  begins  to  fuse.  It  is  then  cooled 
and  weighed  as  silver  chloride. 

GRAVIMETRIC   DETERMINATION    OF   COPPER. 

Copper  may  be  determined  quite  easily  by  electrolysis  of 
the  faintly  acid  (H2SO4)  solution.  The  copper  solution  must  be 
freed  from  other  metals  and  preferably  be  obtained  as  a  solu- 
tion of  copper  sulphate  of  approximately  o.i  of  1%  of  copper. 
50  c.c.  of  such  a  solution  are  put  into  a  platinum  dish  which 
is  placed  upon  a  copper  plate  connected  with  the  negative  pole 
of  a  battery.  A  strip  of  platinum  suspended  from  the  positive 
pole  is  immersed  in  the  solution  and  the  current  allowed  to  pass 
for  from  three  to  twelve  hours,  according  to  the  strength  of  the 
copper  solution.  The  ordinary  no-volt  (direct)  current  em- 
ployed for  electric  lighting  may  be  used  by  introducing  a  re- 


STANDARD  SOLUTIONS  -165 

sistance  of  from  three  to  six  40  watt  lamps.  After  the  copper  has 
been  entirely  deposited  the  residual  solution  is  drained  out  of  the 
platinum  dish,  a  Httle  alcohol  added,  which  is  also  drained  out, 
and  by  setting  fire  to  the  last  traces  of  alcohol  the  precipitated 
copper  is  dried  and  in  condition  to  weigh.  Care  must  be  taken 
to  avoid  oxidation  of  the  finely-divided  copper;  if  it  turns  black 
too  much  heat  has  been  used  and  partial  oxidation  has  taken 
place,  which  has,  of  course,  resulted  in  an  increase  of  weight. 

GRAVIMETRIC   DETERMINATION    OF    ZINC. 

Zinc  may  be  determined  gravimetrically  by  precipitation  as 
zinc  sulphide  as  follows :  To  a  measured  portion  of  the  solution, 
free  from  all  metals  (except  zinc)  of  Groups  I,  II,  III,  and  IV, 
add  ammonium  chloride,  ammonium  hydroxide,  and  ammonium 
sulphide,  as  in  qualitative  analysis.  Filter  the  precipitated 
zinc  sulphide  on  to  counterpoised  filters,  wash  thoroughly  with 
water  containing  a  Httle  ammonium  sulphide,  dry  in  an  atmos- 
phere free  from. oxygen  (hydrogen  or  hydrogen  sulphide),  and 
weigh  as  zinc  sulphide. 

Gravimetric  Assay  or  Gold  and  Silver  in  the  Dry  Way. 

It  is  often  more  convenient  to  determine  gold  and  silver  by 
the  fire  assay  than  by  the  volumetric  methods  previously  given. 
This  is  accomplished  usually  by  fusion  with  an  excess  of  lead 
and  a  borax  flux.  The  mixture  is  kept  at  a  high  heat  for  up- 
wards of  thirty  minutes,  with  a  current  of  air  passing  over  the 
surface  of  the  molten  metals.  This  serves  to  oxidize  and  carry 
away  the  baser  metals,  leaving  the  gold  and  silver  with  but  a 
slight  amount  of  lead,  possibly  a  trace  of  copper  and  tin.  The 
purification  is  completed  by-  cupeUation.  When  the  traces  of 
lead  and  other  metals  are  absorbed  by  the  cupel  or  are  driven 
off  as  volatile  oxides,  the  button  of  gold  and  silver  is  next  cooled 
very  slowly  and  carefully  weighed.  From  this  the  silver  may  be 
dissolved  by  nitric  acid  unless  the  gold  is  in  considerable  excess, 


l66  VOLUMETRIC  ANALYSIS 

which  would  rarely  be  the  case.  If  it  happens  that  the  gold 
is  present  in  sufficient  quantity  to  prevent  the  solution  of  the 
silver  in  nitric  acid  a  known  weight  of  pure  silver  may  be  added 
in  amount  sufficient  to  increase  the  percentage  of  silver  to 
seventy-five  or  over,  fused,  and  then  all  the  silver  dissolved  out 
with  nitric  acid,  leaving  the  gold. 

The  gold  which  has  resisted  solution  may  be  found  as  small 
black  particles  or  grains  in  the  bottom  of  the  crucible.  This 
should  be  carefully  washed  with  distilled  water  by  decantation, 
very  carefully  dried  and  brought  to  a  red  heat,  which  will  give 
a  button  of  pure  gold.  This  may  be  weighed  and  the  weight 
subtracted  from  the  weight  of  gold  and  silver  button  previously 
obtained. 

QUANTITATIVE  ANALYSIS   OF   DENTAL  ALLOYS 
CONTAINING  Au,  Sn,  Ag,  Cu,  Zn. 

Weigh  accurately  0.5  gram  of  alloy  which  has  been  reduced 
to  fine  filings  and  from  which  all  particles  of  iron  have  been 
carefully  removed  by  a  magnet,  transfer  to  a  beaker,  and  dis- 
solve in  15  c.c.  of  strong  HNO3  and  10  c.c.  of  HoO  by  aid  of 
gentle  heat.  If  the  sample  contains  tin  or  gold,  complete  solu- 
tion will  not  be  effected,  but,  by  watching  the  character  of  the 
sediment  through  the  bottom  of  the  beaker,  it  is  possible  easily 
to  determine  when  the  alloy  has  been  completely  disintegrated. 

If  silver  is  to  be  determined  by  titration  with  NaCl  and 
K2Cr04,  evaporate  on  a  water-bath  till  all  nitric  acid  has  been 
expelled. 

If  silver  is  to  be  determined  by  the  sulphocyanate  solution, 
evaporation  at  this  point  is  not  necessary.  In  either  case,  make 
the  whole  solution  up  to  250  c.c.  with  distilled  water;  then  filter 
out  tin  and  gold,  following  the  method  given  under  gravimetric 
determination  of  tin  (page  163),  reserving  the  filtrate  before  any 
wash-water  has  been  added.  For  convenience  this  filtrate  may  be 
marked  "A."     Titrate  this  filtrate  C' A  ")  for  silver  as  follows: 


STANDARD  SOLUTIONS  lt^ 

Take  a  measured  volume,  about  30  c.c,  and  place  in  a  por- 
celain dish  with  ferric  alum  as  indicator. 

Then  place  the  standard  KCyS  in  the  burette  and  titrate 
till  the  faint  red  color  is  produced. 

Suppose  8  c.c.  of  KCyS  is  used.  The  weight  of  silver  in  i  c.c. 
of  a  decinormal  solution  is  0.0108  gram.  Multiplying  8  by 
0.0108  =  0.0864.  Divide  by  number  of  c.c.  of  solution  taken, 
0.0864  -^  30  =  0.00288  gram  Ag  in  i  c.c.  of  solution. 

Multiply  by  whole  number  of  cubic  centimeters  and  divide 
by  weight  of  alloy  taken  and  result  will  be  percentage  of  silver. 

Take  100  c.c.  of  filtrate  "  A  "  and  precipitate  silver  by  slight 
excess  of  HCl.  Filter  and  wash  precipitate  thoroughly  with 
warm  water.  Concentrate  filtrate  and  wash-water,  which  may 
be  designated  as  filtrate  "  B."  Pass  H2S  gas  into  "  B  "  till 
copper  is  entirely  separated  as  CuS.  Filter  and  wash  CuS 
seven  or  eight  times  with  dilute  H2S  water.  Reserve  filtrate 
and  wash-water  as  filtrate  "  C."  Dissolve  CuS  in  dilute  HNO3, 
wash  paper  carefully,  concentrate,  and  determine  amount  of 
copper  by  deposition  upon  platinum  (page  164).  Concentrate 
filtrate  "  C  "  and  determine  zinc  by  volumetric  method  given  on 
page  162.  Gold  and  tin  in  residue  insoluble  in  nitric  acid  may 
be  determined  by  method  given  on  pages  163  and  158. 

QUESTIONS   IN   VOLUMETRIC   WORK. 

Why  is  an  N/io  solution  of  hydrochloric  acid  more  generally 
serviceable  than  a  similar  solution  of  oxaHc  acid? 

Why  use  nitric  acid  for  titration  of  chlorine  in  urine  by  use 
ofKCNS? 


PART    IV. 

MICROCHEMICAL   ANALYSIS. 

CHAPTER  XVIII. 

METHODS. 

The  advantages  of  microchemistry  are  many,  as  claimed  by 
its  enthusiastic  advocates,  and  there  are  two  particulars  in  which 
these  methods  strongly  recommend  themselves  to  the  dental 
practitioner:  (i)  ]\Iicrocheniical  analysis  deals  with  exceedingly 
minute  portions  of  matter,  making  the  examination  of  very 
small  particles  of  substance  easily  possible.  (2)  Three  or  four 
one-ounce  "  drop-bottles  "  and  a  few  two-drachm  vials  will 
contain  all  necessary  reagents,  and  in  consequence  three  feet 
of  bench-room  will  furnish  ample  laboratory  space. 

The  principles  of  microchemical  analysis  are,  of  course,  the 
same  as  for  any  analysis,  but  the  processes  employed  are  quite 
different  and  need  some  explanation.  In  microchemical  analysis 
the  production  of  crystals  of  characteristic  form  furnishes  per- 
haps the  most  rapid  method  of  detection  of  an  unknown  sub- 
stance, and  in  this  we  are  greatly  aided  by  the  use  of  polarized 
hght,  which  not  only  helps  in  the  differentiation  of  crystals  but 
often  makes  it  possible  to  see  and  distinguish  small  or  trans- 
parent crystals  which  might  otherwise  escape  notice  altogether. 

Use  of  Microscope.  —  For  the  examination  of  the  crystals 
mentioned  in  this  chapter,  also  for  the  work  required  on  saliva 
or  urine,  lenses  of  comparatively  low  power  are  sufl&cient.  For 
most  of  the  microchemical  tests,  a  No.  3  Leitz  or  a  i6-mm.  Bausch 
&  Lomb  objective  \^dll  be  found  satisfactory.     For  a  few  micro- 

168 


METHODS  169 

chemical  tests  and  for  urine,  an  8-mm.  Bausch  &  Lomb  or  a 
No.  5  Leitz  objective  will  give  better  results  in  the  hands  of  a 
beginner  than  one  of  higher  power. 

In  using  the  microscope  for  microchemistry,  the  preparation 
should  ahcays  be  covered  with  a  cover  glass  and  the  examination 
be  made  with  the  low-power  lens  if  possible.  The  object  in 
covering  is  to  prevent  any  action  by  reagent  upon  the  objective. 
As  a  further  precaution,  it  is  well  to  form  the  habit  of  first 
lowering  the  objective  and  then  focusing  by  upward  movement 
of  the  draw-tube. 

Formation  of  crystals  may  be  brought  about  in  two  ways: 
first,  by  precipitating  insoluble  crystalline  salts  by  use  of  re- 
agents, as  in  ordmary  quaHtative  analysis;  second,  by  allowing 
salts  to  crystallize  by-  spontaneous  evaporation  of  the  solvent. 

If  the  first  method  is  to  be  employed  it  is  essential  to  have 
the  dilution  fairly  constant  in  order  to  obtain  crystals  which  shall 
be  comparable  with  those  obtained  at  other  times  or  by  other 
indi\dduals.  The  tendency  of  strong  solutions  is  to  give  amor- 
phous precipitates.  Sometimes  the  precipitate  will  be  amor- 
phous when  first  thrown  down,  but  upon  standing  wiU  assume 
crystalline  form.  To  secure  the  uniformity  of  results  necessary 
to  correct  deductions,  the  follo^\'ing  method  of  procedure  should 
be  exactly  followed  every  time. 

The  reagent  should  be  of  uniform  strength,  usually  one  or 
two  per  cent.  Place  on  a  clean  microscope-slide  a  small  drop  of 
the  solution  to  be  tested,  and  as  close  as  possible  without  touching 
it,  one  of  about  equal  size  of  the  reagent  to  be  used.  Now  bring 
the  drops  together  by  tapping  the  slide  or  with  a  small  glass  rod. 
If  a  precipitate  forms  immediately,  cover  with  a  cover-glass  (this 
must  always  be  done)  and  examine  wath  the  microscope.  If  the 
precipitate  is  crystalline,  note  the  form,  and  in  any  case,  whether 
crystalline  or  not,  repeat  the  test  after  diluting  the  unknowTi 
solution  one-half.  If  the  second  test  gives  an  amorphous  pre- 
cipitate, or  crystals  of  different  shape  from  the  first,  continue 


I70  MICROCHEMICAL  ANALYSIS 

the  dilution  of  the  unknown  till  a  point  is  reached  when  admixture 
with  the  drop  of  reagent  gives  no  immediate  precipitate,  but  one 
appearing  in  a  few  seconds'  time  (five  to  thirty).  In  this  way 
we  have  produced  the  precipitate  under  standard  conditions  or 
as  nearly  such  as  is  possible  with  unknown  solutions. 

Until  thoroughly  familiar  with  the  forms  obtained  by  drying 
the  various  reagents,  it  is  well  to  evaporate  a  small  drop  of  the 
reagent  alone,  on  the  same  shde  on  which  a  test  is  made,  for  the 
sake  of  subsequent  comparisons. 

Filtration  in  microchemical  examinations,  when  perhaps  only 
a  few  drops  of  solution  are  to  be  had,  may  be  effected  in  a  very 
satisfactory  manner  and  without  appreciable  loss  by  absorption 
as  follows: 

Cut  a  filter-paper  about  i  cm.  wide  and  6  cm.  long,  double 
it  and  crease  the  middle  so  that  it  assumes  the  shape  of  an  in- 
verted V.  Put  the  solution  to  be  filtered  in  a  small  watch- 
glass  placed  at  a  slight  elevation  above  a  microscope  slide; 
now  place  one  "  leg  "  of  the  strip  of  filter-paper  in  the  watch- 
glass,  allowing  the  end  of  the  other  to  touch  the  slide.  By  capil- 
lary attraction  the  clear  solution  will  follow  over  the  bend 
in  the  strip  of  paper  and  a  drop  or  two  of  perfectly  clear  filtrate 
suitable  for  the  test  will  be  found  upon  the  shde. 

Evaporation  of  a  solution  is  best  effected  on  a  small  watch- 
glass  held  in  the  fingers  and  moved  back  and  forth  over  a  low 
Bunsen  flame,  or  else  placed  over  a  water-bath. 

The  purpose  of  the  microchemical  tests  here  outhned  is  not 
so  much  a  method  of  general  qualitative  analysis,  to  which  they 
are  not  suited,  as  it  is  a  specific  appHcation  of  well-known  reac- 
tions to  concrete  examination  of  substances,  the  uses  and  prob- 
able composition  of  which  are  known.  The  details  of  the  various 
tests  will  be  given  under  classification  furnished  by  the  sub- 
stances investigated. 

Our  study  may  include  alloys  and  amalgams,  teeth,  tartar, 
dental   anesthetics,    cement,   mouth-washes,   antiseptics,   disin- 


PLATE   II.  — MICROCHEMICAL   ANALYSIS. 


Fig.  I. 
Calcium  Oxalate. 


Fig.  3. 
Strontium  Oxalate. 


Fig.  2. 
Cadmium  Oxalate. 


Fig.  4. 
Sodium  Oxalate  (P.L. 


Fig.  5. 
Oxalate  of  Urea. 


Fig.  6. 
Zinc  Oxalate. 


PLATE  III.  — MICROCHEMICAL   ANALYSIS. 


Fig.  I. 

Ammonium  Platinic  Chloride. 


Fig.  2. 
/3  Eucaine  and  Plalinic  Chloride. 


Fig.  3. 
Potassium  Platinic  Chloride. 


Fig.  4. 
Cocaine  and  Potassium  Permanganate. 


Fig.  5. 
Tri-brom-phenol. 


Fig.  6. 
^lorphine. 


METHODS  171 

fectants,  and  sediments  obtained  from  the  saliva  and  from  the 
urine. 

The  following  crystals  are  selected  as  among  those  most 
frequently  met  with  in  the  analysis  of  the  above  substances  or 
best  suited  for  the  study  of  microchemical  processes,  and  the 
student  should  make  each  test  here  indicated  and  carefully  draw 
the  crystals  produced: 

1.  Calcium  oxalate  from  2%  H2C2O4  and  CaCl2  solutions 
(Plate  II,  Fig.  i). 

2.  Cadmium  oxalate  from  2%  H2C2O4  and  CdS04  solutions 
(Plate  II,  Fig.  2). 

3.  Strontium  oxalate  from  2%  H2C2O4  and  Sr(N03)2  solutions 
(Plate  II,  Fig.  3). 

4.  Sodium  oxalate  by  evaporation  of  aqueous  solution,  also 
by  evaporation  of  urine  containing  Na2C204  (polarized  light) 
(Plate  II,  Fig.  4). 

5.  Urea  oxalate  from  2%  H2C2O4  and  urea  solution  (Plate 

11,  Fig.  5). 

6.  Ammonium-magnesium-phosphate  from  magnesium  mix- 
ture *  and  sodium  phosphate  (Plate  IV,  Fig.  2). 

7.  Ammonium  platinic  chloride  (Plate  III,  Fig.  i).  For 
preparation  of  crystals  see  pages  46  and  47. 

8.  Potassium  platinic  chloride,  Il2PtCl6  (Plate  III,  Fig.  3). 
For  preparation  of  crystals  see  page  47. 

9.  Sodium  urate  by  evaporation  (polarized  light)  (Plate  X, 

Fig.  3^  OPP-  page  255). 

10.  Crystals  formed  from  cocaine  and  potassium  perman- 
ganate (Plate  III,  Fig.  4). 

11.  Crystals  formed  from  phenol  and  dilute  bromine  water 
(tribromphenol)  (Plate  III,  Fig.  5). 

12.  Crystals  formed  from  morphine  solutions  and  ammonia 
(morphia)  (Plate  III,  Fig.  6). 

*  Magnesium  mixture  as  used  in  urine  analysis  to  precipitate  phosphates 
contains  MgCU  (or  MgSOi) ,  NH4CI,  and  NH4OH. 


172  MICROCHEMICAL  ANALYSIS 

13.  Crystals  formed  from  morphine  and  Marme's  reagent 
(Plate  IV,  Fig.  i). 

14.  Platinum  chloride  and  /3-eucaine  (Plate  III,  Fig.  2). 

15.  'Stovaine  and  platinum  chloride  (Plate  IV,  Fig.  4.). 

16.  Alypin  and  KI  (Plate  IV,  Fig.  6). 

The  list  may  be  extended  to  include  the  crystals  produced 
by  various  alkaloidal  salts  with  the  common  reagents,  also  sub- 
stances usually  employed  in  the  manufacture  of  the  various 
dental  preparations. 


PLATE  IV.— MICR0CHEM1C.\L  /VNALYSIS. 


Fig.   I. 
]\Iorphine  and  Marme's  Reagent. 


Fig.  2. 
Magnesium  Ammonium  Phosphate. 


Fig.  3. 
Cocain  with  Tin  Chloride. 


Fig.  4- 

Stovaine  and  Platinic  Chloride.  _ 


Fia  5. 
Palmitic  Acid. 


Fig.  6. 

Al}-pin  and  Potassium  Iodide. 


CHAPTER  XIX. 
LOCAL  ANESTHETICS   AND   ANTISEPTICS. 

(Also  some  other  substances  commonly  used  in  dental  preparations.) 

In  considering  the  chemistry  of  local  anesthetics  we  may- 
divide  them  into  two  classes  as  follows : 

First,  those  of  definite  or  well-known  composition,  and 

Second,  preparations  of  a  proprietary  nature,  the  compo- 
sition of  which  is  always  problematical. 

In  the  first  class  will  be  found  cocaine,  eucaine,  tropacocaine, 
acoin,  ethyl  chloride,  etc.,  which  will  be  later  alphabetically 
considered.  The  second  class  contains  a  large  number  of  prep- 
arations of  all  degrees  of  value,  among  them  some  of  exceeding 
merit  and  largely  used,  others  of  doubtful  worth,  some  worth- 
less if  not  dangerous.  Many  of  the  preparations  of  this  class 
contain  cocaine  as  the  anesthetic,  and  frequently  a  little  nitro- 
glycerin as  a  cardiac  stimulant  to  counteract  the  depressant 
effect  of  the  alkaloid.  Carbolic  acid  and  oil  of  cloves  are  also 
frequently  used. 

Many  of  the  constituents  of  this  class  of  anesthetics  may 
readily  be  identified  by  the  processes  of  microchemical  analysis 
to  which  previous  reference  has  been  made;  others  may  be  de- 
tected by  special  tests,  some  of  which  are  given  under  the  various 
substances  in  the  following  list.  This  Hst  has  been  extended 
to  include  a  considerable  number  of  preparations  of  common 
occurrence. 

Acoin,  a  synthetic  compound,  chemically  diparanisyl-mono- 

.  \  I   /  (NC6H40CH3)2  \  \ 

phenetyl-guanidine     hydrochloride      (C  HClj 


^  (NC6H4OC2H5)  ^ 


173 


174  MICROCHEMICAL  ANALYSIS 

soluble  in  both  alcohol  and  water.  Strongly  antiseptic  and  a 
valuable  anesthetic,  especially  in  conjunction  with  cocaine. 
Acoin  should  be  used  only  in  solution  and  this  should  be  kept 
in  a  dark  place. 

Adrenalin,  a  valuable  hemostatic  and  frequently  used  in  con- 
junction with  dental  anesthetics,  is  the  active  principle  of  the 
suprarenal  gland  or  capsule.  It  occurs  as  very  small  white 
crystals  which  are  not  very  stable  and  only  slightly  soluble 
in  water,  hence  the  article  is  usually  sold  in  solution  with  sodium 
chloride,  according  to  the  following  formula  taken  from  a  com- 
mercial sample: 

Adrenalin  chloride,  i  part;  normal  sodium  chloride  solution 
(with  0.5%  chloretone),  1000  parts.  This  solution  is  usually 
diluted  with  the  normal  (0.6%)  salt  solution.  According  to  the 
Druggists'  Circular,  preparations  similar  to  the  above  are  also 
marketed  under  the  names  of  adrenol,  adnephrin,  hemostatin, 
suprarenalin  (Armour  &  Co.),  suprarenin,  etc.,  see  Epinephrine. 

Alypin.  —  Benzoyl  -  dimethylamino  -  methyl-dimethylamino- 
butane  hydrochloride,  white  crystalline,  hygroscopic,  melts  at 
169°  C.     Soluble  in  water  and  alcohol. 

Alypin  can  be  steriHzed  without  decomposition,  is  not  half 
so  poisonous  as  cocaine  and  is  cheaper.  Is  used  in  2%  solution. 
Solution  should  be  freshly  made  and  prolonged  boiling  avoided. 
Sometimes  used  with  adrenalin.     (Cosmos,  1908,  p.  889.) 

Alypin  nitrate  occurs  as  a  white,  crystalline  powder  melting 
at  159°  C,  readily  soluble  in  ether.  Mfrs,:  Farbenfabriken  of 
Elberfeld,  Elberfeld  (Germany)  and  New  York.  (Mod,  Mat, 
Med.,  page  21.) 

Test.  —  Alypin  gives  needle-shaped  crystals  with  potassium 
iodide,  easily  produced.     (Plate  IV,  Fig.  6.) 

Ammonium  Bifluoride  is  strongly  recommended  as  a  solvent 
for  tartar  by  Dr.  Joseph  Head  of  Philadelphia.  In  Items  of 
Interest,  Vol.  31,  page  174,  Dr.  Head  gives  the  following  method 
for  its  preparation.     Hydrofluoric  acid  is  neutralized  with  am- 


LOCAL  ANESTHETICS  AND  ANTISEPTICS  .175 

monium  carbonate,  the  solution  filtered  and  evaporated  to  half 
its  bulk,  the  original  volume  restored  by  adding  more  hydro- 
fluoric acid  and  then  the  resulting  mixture  is  again  concentrated 
to  half  its  volume  by  evaporation. 

Anesthol,  or  Anaesthol,  is  a  mixture  of  ethyl  chloride  and 
methyl  chloride,  used  as  a  local  dental  anesthetic.  The  name  is 
also  applied  to  a  general  anesthetic  given  by  inhalation  and  con- 
sisting of  a  mixture  of  ethyl  chloride  17  parts,  chloroform  35.89 
parts,  and  ether  47.1  parts. 

Anaestheaine,  a  local  anesthetic,  contains  five  grains  of 
stovaine  to  the  fluid  ounce. 

Argyrol,  a  protein  compound  of  silver,  occurs  as  dark  brown 
crystals  containing  30%  of  silver.  It  is  easily  soluble  in  water. 
It  does  not  precipitate  chlorine  nor  coagulate  albumin,  and  is 
recommended  for  use  in  place  of  ordinary  silver  nitrate. 

Aristol  is  given  by  the  U.  S.  D.  as  a  synonym  for  dithymol- 
diiodide  which  contains  45%  of  iodine  and  is  used  as  an  anti- 
septic similarly  to  iodoform. 

Atropine,  an  alkaloid  obtained  from  belladonna,  usually  used 
combined  with  sulphuric  acid,  (Ci7H23N03)2H2S04;  the  alkaloid 
is  only  sparingly  soluble  in  water  but  the  sulphate  is  easily  sol- 
uble, dissolving  in  about  one-half  part  of  water  at  ordinary  tem- 
perature. A  one  per  cent,  solution  is  said  to  produce  complete 
insensibility  of  the  nerves  in  cases  in  which  an  artificial  tooth  is 
inserted  in  a  living  root.     (U.  S.  D.,  page  249.) 

Tests.  —  Atropine  may  be  separated  from  a  local  anesthetic 
by  first  rendering  the  mixture  alkaline  with  ammonia  and  shaking 
with  chloroform.  Upon  evaporation  of  the  chloroform  solution 
on  a  watch-glass  the  resulting  residue  may  be  tested  by  adding 
a  drop  or  two  of  sulphuric  acid  and  a  trace  of  potassium  bichro- 
mate and  a  little  water.  The  odor  of  bitter  almonds  is  produced, 
A  more  conclusive  test  is  to  convert  the  alkaloid,  which  has 
been  dissolved  by  the  chloroform,  into  a  salt  by  the  addition  of  a 
few  drops  ot  acetic  acid,  evaporating  to  complete  dryness,  taking 


176  MICROCHEMICA L  ANAL YSIS 

up  in  a  few  drops  of  distilled  water  and  placing  one  or  two  drops 
of  this  solution  in  the  eye  of  a  cat,  when,  if  atropine  is  present,  a 
dilation  of  the  pupil  occurs  in  from  fifteen  minutes  to  an  hour 
and  a  half,  according  to  amount  present. 

Borax.  —  Sodium  tetraborate,  Na2B407,  is  used  in  antiseptic 
solutions  and  may  be  detected  as  follows:  evaporate  a  Httle  of 
the  solution  to  dryness,  add  a  little  HCl,  evaporate  to  dryness 
a  second  time,  then  add  a  very  dilute  HCl  solution  containing 
tincture  turmeric.  Upon  drying  this  mixture  a  beautiful  pink 
color  appears.  If  much  organic  matter  is  present  it  may  be 
burned  off  in  the  Bunsen  flame  before  the  addition  of  any 
acid. 

Carbolic  Acid.  —  See  Phenol. 

Chloral  Hydrate,  CCI3CHO.H2O,  a  crystalline  solid  com- 
posed of  trichloraldehyde,.or  chloral,  with  one  molecule  of  water 
(U.  S.  P.),  easily  soluble  in  water,  may  become  with  alcohol  a 
chloral  alcoholate  comparatively  insoluble  in  water. 

Tests.  —  Chloral  may  be  detected  by  adding  to  the  sus- 
pected mixture  a  few  cubic  centimeters  of  fairly  strong  alco- 
holic solution  of  KOH  or  NaOH  with  one  drop  of  aniline  oil  and 
heating,  when  isobenzonitril  is  produced,  which  has  a  peculiarly 
disagreeable  and  characteristic  odor.  This  test  is  also  given 
by  chloroform,  wliich  is  produced  by  heating  chloral  hydrate 
with  caustic  alkaU.  If  more  than  traces  of  chloral  are  present 
this  latter  reaction  may  be  a  sufficient  test. 

Chloretone,  CCl3COH(CH3)2,  is  the  commercial  name  of 
acetone-chloroform  or  tertiary  trichlorbutyl  alcohol.  Made 
from  chloroform,  acetone,  and  an  alkali,  and  occurs  as  small 
white  crystals,  with  taste  and  odor  like  camphor.  It  is  dissolved 
by  alcohol  and  glycerol  and  to  a  slight  extent  by  water. 

Chloroform,  trichlormethane,  CHCI3,  prepared  by  action  of 
chlorinated  hme  on  acetone.  Chloroform  is  a  heavy  colorless 
liquid  with  a  specific  gravity  of  1.490  at  15°  C.  Is  very  volatile 
and   used   as   a   solvent   for   gutta-percha,   caoutchouc,   many 


LOCAL  ANESTHETICS  AND  ANTISEPTICS  177 

vegetable    balsams,    camphor,    iodine,    bromine,    and    chlorine; 
it  also  dissolves  sulphur  and  phosphorus  to  a  limited  extent. 

Tests.  —  It  may  be  detected  by  its  odor,  when  heated,  or  by 
the  isobenzonitril  test  to  which  reference  has  been  made  under 
chloral  hydrate. 

Cocaine  is  the  alkaloid  obtained  from  erythroxylon  coca. 
The  hydrochlorate,  C17H21NO4HCI,  is  the  salt  most  usually 
employed.  This  is  easily  soluble  in  water  and  very  largely 
used  as  a  dental  anesthetic  in  a  one  or  two  per  cent,  solution. 

Tests.  —  Cocaine  solutions  respond  to  the  usual  alkaloidal 
reagents.  With  1%  solution  potassium  permanganate  gives 
pink  plates  resembling  cholesterol  (Plate  III,  Fig.  4)  in  form 
but  not  in  color. 

Dilute  cocaine  solution  with  picric  acid  gives  a  yellow  pre- 
cipitate which  becomes  crystalline  on  standing.  Quite  char- 
acteristic crystals  may  also  be  obtained  from  dilute  cocaine 
solutions  and  stannous  chloride  in  the  presence  of  free  HCl. 

Creosote.  —  A  mixture  of  phenols  derived  from  the  destruc- 
tive distillation  of  wood  tar.  It  is  a  hea\'y^  oily  liquid  acting 
when  pure  as  an  escharotic.  It  is  analogous  in  many  respects 
to  carbolic  acid  and  may  be  used  for  similar  purposes.  To 
distinguish  between  creosote  and  carbolic  acid,  boil  with  nitric 
acid  until  red  fumes  are  no  longer  given  off.  Carbohc  acid  will 
give  yeUow  crystalline  deposit;  creosote  wall  not.  An  alco- 
holic solution  of  creosote  is  colored  emerald  green  by  an  alcoholic 
solution  of  ferric  chloride.     Phenol  is  colored  blue. 

Cresol  is  the  next  higher  homologue  to  phenol,  ha\dng  a 
formula  C6H4CH3OH,  boiling  at  198°  C.  It  is  largely  used, 
usually  together  with  allied  compounds  from  coal-tar,  as  anti- 
septic and  disinfectant  solutions. 

Ektogan.  —  Peroxide  of  zinc,  Zn02,  designed  for  external 
use. 

Epinephrine.  —  The  active  principle  is  the  suprarenal 
glands.     Chemically  it  is  an  o-dihydroxyphenyl-ethanolmethyl- 


178  MICROCHEMICAL  ANALYSIS 

amine,  C6H3(OH)2.CHOH.CHoNHCH3.  This  is  a  weak  base 
which  combines  with  hydrochloric  acid  to  form  the  hydrochlo- 
ride in  which  form  it  is  usually  used  in  dilutions  of  one  part  to  a 
thousand.  It  acts  as  a  cardiac  stimulant  causing  rise  in  blood 
pressure  with  slower  heart  action,  acting  somewhat  in  the  same 
way  as  digitalis. 

Ethyl  Chloride,  monochlorethane,  C2H5CI.  This  is  a  gaseous 
substance  at  ordinary  temperature,  but  when  used  as  a  dental 
anesthetic  it  is  compressed  to  a  colorless  liquid  which  has  a 
specific  gravity  of  0.918  at  8°  C,  is  highly  inflammable  and  usu- 
ally sold  in  sealed  glass  tubes  of  from  ten  to  thirty  grams 
each. 

p-Eucaine  is  the  hydrochlorate  of  bezoylvinyldiacetone- 
alkamine,  and  occurs  as  a  white,  neutral  powder,  soluble  in 
about  thirty  parts  of  cold  water.  It  is  used  like  cocaine  as  a  local 
anesthetic,  and  is  claimed  to  be  less  toxic,  and  sterilizable  by 
boihng  without  danger  of  decomposition.  It  is  usually  appHed 
in  from,  one  to  five  per  cent,  solutions,  which  are  conveniently 
prepared  in  a  test-tube  with  boiling  water.  It  is  also  marketed 
in  the  form  of  i|  and  5-grain  tablets.     (Druggists'  Circular.) 

Test.  —  /3-Eucaine  gives  characteristic  crystals  with  platinic 
chloride.     (Plate  III,  Fig.  2.) 

Eucain  Lactate.  —  "  Eucain  lactate  is  used  in  two  to  five  per 
cent,  solution  as  a  local  anesthetic  in  ophthalmic  and  dental  prac- 
tice and  in  ten  to  fifteen  per  cent,  solution  when  used  in  the  nose 
or  ear."     (Review  of  American  Chemical  Research,  page  97, 

1905-) 

Eudrenin    is    a   local   anesthetic   marketed   in   capsules   of 

0.5  c.c.  containing  1/12  grain  of  eucain  and  1/4000  grain  of 
adrenaHn  hydrochloride.  It  is  used  as  a  local  anesthetic, 
chiefly  in  dentistry.  The  contents  of  one  or  two  capsules,  ac- 
cording to  the  number  of  teeth  to  be  extracted,  are  injected  into 
the  gums  ten  minutes  before  extraction.  Mfrs. :  Parke,  Davis  & 
Co.,  Detroit,  Mich.     (Mod.  Mat.  Med.,  page  147.) 


LOCAL  ANESTHETICS  AND  ANTISEPTICS  179 

Eugenol,  C10H12O2,  synthetical  oil  of  cloves.  Eugenol  is  mis- 
cible  with  alcohol  in  all  proportions.  Exposure  to  air  thickens 
and  darkens  it.  Should  be  kept  in  well-stoppered  amber-colored 
bottles  (U.  S.  D.). 

Europhen  —  recommended  by  Dr.  J.  P.  Buckley  as  a  sub- 
stitute for  iodoform  (Dental  Review,  Vol.  21,  page  1284). 

Di-iso-butyl-cresol  is  described  as  a  bulky  yellow  powder  of 
faint  saffron  odor  and  containing  28%  of  iodine.  (Mod.  Mat. 
Med.,  page  152.) 

Formaline,  Formol,  Formine,  etc.,  are  commercial  names  for 
a  40%  aqueous  solution  of  formaldehyde,  HCHO,  prepared 
by  the  partial  oxidation  of  methyl  alcohol.  FormaUne  is  a  power- 
ful disinfectant  very  generally  used.  (For  test  see  page  386, 
Exp.  83.) 

Glycerol  is  a  triatomic  alcohol,  C3H5(OH)3,  a  colorless  liquid 
of  syrupy  consistence  and  sweetish  taste,  specific  gra\ity  1.250 
at  15°  C.     It  is  easily  soluble  in  either  water  or  alcohol. 

Tests.  —  Upon  heating  with  acid  potassium  sulphate  (solid) 
it  is  decomposed,  giving  off  odor  of  acrolein,  which  is  usually 
sufficient  for  its  identification.  A  further  test  may  be  made  by 
moistening  a  borax  bead  on  a  platinum  wire  with  the  suspected 
solution  (after  concentration)  and  holding  in  a  non-luminous 
flame,  to  which  it  will  give  a  deep-green  color  which  does  not 
persist.  Glycerol  when  present  is  apt  to  interfere  with  charac- 
teristic crystaUization  of  many  precipitates. 

Gram's  Solution,  Kuhne's  modification,  contains  two  grams 
of  iodine,  and  four  grams  potassium  iodide  in  100  c.c.  of  water. 

Gutta-percha.  —  The  name  signifies  scraps  of  gum.  It  is  ob- 
tained as  a  milky  exudate  from  a  number  of  tropical  trees.  It 
is  soluble  in  ether,  chloroform,  carbon  disulphide,  toluene,  and 
petroleum  ether.  It  may  be  freed  from  impurities  by  shaking 
the  solution  with  calcium  sulphate,  which  will  mechanically  carry 
coloring  matter  and  other  impurities  with  it  as  it  slowly  settles 
out  from  the  mixture.     It  is  not  soluble  in  alcohol  or  in  water. 


l8o  MICROCHEMICAL  ANALYSIS 

Heroin  is  a  diacetic  ester  of  morphine.  It  is  usually  ob- 
tained as  the  hydrochloride  and  occurs  as  a  white  powder,  solu- 
ble in  two  parts  of  water.  Its  action  is  similar  to  that  of  mor- 
phine; it  answers  to  the  usual  color  tests  for  morphine,  but  may 
be  distinguished  from  it  by  the  fact  that  it  will  yield  acetic  ether 
upon  heating  with  alcohol  and  sulphuric  acid. 

Hopogan  (also  known  as  biogen)  is  a  peroxide  of  magnesium, 
Mg02,  recommended  as  a  non-poisonous  and  non-astringent 
intestinal  germicide. 

Hydrogen  Peroxide,  or  dioxide,  H2O2,  is,  when  pure,  a  syrupy 
liquid  without  odor  or  color.  It  is  sold  under  various  trade 
names  in  aqueous  solution  containing  about  3%  and  yielding 
upon  decomposition  about  10  volumes  of  oxygen  gas.  It  is 
used  also  as  an  escharotic  in  etherial  solutions  containing  twenty- 
five  to  fifty  per  cent.  H2O2.  Peroxide  solutions  may  be  concen- 
trated by  heat  without  decomposition  if  kept  perfectly  free  from 
dirt  or  traces  of  organic  matter.  It  is  readily  prepared  by  treat- 
ment of  metallic  peroxides,  as  Ba02  with  dilute  acids. 

Ba02  -f  H2SO4  =  BaS04  +  H2O2 
or  Ba02  +  H2O  -\-  CO2  =  BaCOs  -f  H2O2. 

This  latter  reaction  has  the  advantage  of  producing  an  insolu- 
ble barium  compound  and  at  the  same  time  introducing  no 
objectionable  acid.  The  peroxides  of  sodium,  calcium,  magne- 
sium, and  zinc  may  also  be  used;  Zn02,  however,  is  compara- 
tively expensive  and  used  in  powder  form  as  an  antiseptic 
dressing  rather  than  as  a  source  of  H2O2.  Na202  is  valuable  as 
a  bleaching  agent,  because  for  this  purpose  an  alkaline  solution 
is  required  and  the  solution  of  Na202  in  water  produces  both 
alkali  and  H2O2  according  to  the  following  reaction: 

Na^Os  +  2  H2O  =  2  NaOH  -f  H2O2. 

Sodium  perborate  (page  185),  also  sold  as  euzone,  is  a  powder 
which  will  produce  H2O2  in  water.     Commercial  H2O2  solutions 


LOCAL  ANESTHETICS  AND  ANTISEPTICS  i8l 

are  usually  acid  in  reaction,  as  such  solutions  are  more  stable 
than  if  neutral  or  alkaline. 

Test.  —  Add  to  a  solution  of  H2O2  a  few  drops  of  bichromate 
of  potassium  solution  and  a  little  dilute  H2SO4.  Shake  cold  with 
a  little  ether  in  a  test-tube.  The  ether  should  be  colored  blue. 
(For  further  tests  see  experiments.) 

Lugol's  Caustic  Iodine  is  made  of  iodine  and  potassium  iodide, 
one  part  of  each  dissolved  in  two  parts  of  water. 

Lugol's  Iodine  Solution.  —  See  appendix  under  Iodine  Solu- 
tion. 

Menthol  is  the  stearopten  obtained  from  the  oil  of  pepper- 
mint. It  is  a  volatile  crystalline  substance  having  a  formula 
C6H9OHCH3C3H7.  Menthol  is  but  shghtly  soluble  in  water 
but  freely  soluble  in  alcohol,  ether,  chloroform,  or  glacial  acetic 
acid.  The  presence  of  menthol  may  usually  be  detected  by  its 
odor.  If  the  odor  should  be  suggestive  but  not  distinctive 
it  is  well  to  place  a  Httle  of  the  substance  on  a  filter-paper,  rub 
it  between  the  thumb  and  finger,  thereby  obtaining  a  "  fractional 
evaporation,"  when  the  more  easily  volatile  substance  will  pass 
ofif  first,  thus  producing  a  partial  separation  of  substances. 

Mercuric  Chloride,  corrosive  sublimate,  HgClo,  is  soluble  in 
about  sixteen  parts  of  water  and  three  parts  of  alcohol.  It  is  a 
powerful  antiseptic,  in  aqueous  solution  i/iooo  to  1/5000,  but 
should  never  be  used  in  mouth- washes. 

Tests.  —  A  drop  of  the  suspected  solution  with  a  trace  of 
potassium  iodide  will  give  a  red  precipitate  of  mercuric  iodide 
soluble  in  excess  of  either  reagent.  With  lime-water  or  fixed 
alkaline  hydroxides  a  black  precipitate  is  produced.  A  drop  of 
mercurial  solution  placed  on  a  bright  copper  plate  will  leave 
a  tarnished  spot  vdue.  to  the  reduction  of  the  mercuric  salt  and 
subsequent  amalgamation  of  the  metal. 

Methethyl.  —  Ethyl  chloride  mixed  with  a  little  methyl 
chloride  and  chloroform  is  said  to  be  the  composition  of  a  local 
anesthetic  sold  under  the  name  of  methethyl  (U.  S.  D.). 


l82  MICROCIIEMICAL  ANALYSIS 

Methyl  Chloride,  CH3CI,  is  a  colorless  gas  which  condenses  to 
a  liquid  at  23°  C.  Methyl  chloride  is  easily  soluble  in  alcohol, 
somewhat  in  water,  and  is  used  in  a  similar  manner  to  ethyl 
chloride. 

Morphine,  C17H19NO3,  alkaloid  from  opium.  Solutions  for 
use  are  made  from  the  sulphate,  hydrochlorate,  or  acetate.  The 
alkaloid  itself  is  insoluble  in  water;   its  salts  are  easily  soluble. 

Morphine  may  be  separated  from  solutions  containing  it  by 
making  the  solution  alkaline  with  ammonia,  and  shaking  out 
the  precipitated  alkaloid  with  warm  ethyl  acetate.  Upon 
evaporation  of  the  solvent  the  residue  may  be  tested  with 
Frohde's  reagent  (sodium  molybdate,  1%,  in  strong  sulphuric 
acid).  The  color  obtained  should  be  a  violet,  changing  usually 
to  brown;  a  pure  blue  color  is  not  distinctive  for  morphine.  If 
the  morphine  solution  is  of  sufficient  strength  the  addition  of  am- 
monia will  produce  minute  crystals  of  the  alkaloid  as  shown  on 
Plate  III,  Fig.  6.  Dental  anesthetics  containing  morphine  will 
give  precipitates  with  the  usual  alkaloidal  reagents.  Marme's 
reagent  (Cdl2)  gives  crystals  represented  on  Plate  IV,  Fig.  i. 

Nirvanin,  hydrochloride  of  diethyl-glycocoll-/?-amino-o-oxy- 
benzoic-methylester,  of  the  formula 

(CH2N)    =    (C2H5).2HC1 

I 
CO.NH.C6H3(OH)COOCH3. 

White  prisms  soluble  in  water  and  in  alcohol,  melt  at  185°  C, 
violet  reaction  with  ferric  chloride. 

Nitroglycerin,  C3H5(N03)3,  is  used  as  a  cardiac  stimulant 
in  alcoholic  solution,  the  U.  S.  P.  Spiritus  Glonoini,  containing 
1%  by  weight  of  the  substance. 

Test.  —  Extract  the  dry  substance,  or  the  evaporated  residue, 
with  alcohol.  Filter  and  evaporate  to  dryness.  Add  i  c.c.  of 
sulphuric. acid  and  i  c.c.  of  phenoldisulphonic  acid.  Heat  over 
a  water  bath  for  five  minutes;  add  water  and  excess  of  ammonia. 


LOCAL  ANESTHETICS  AND  ANTISEPTICS  183 

A  deep  yellow  color  of  ammonium  picrate  indicates  nitrates  in 
the  original  substance.     Exp.  No.  148,  p.  397. 

Novocaine,  discovered  by  Uhlf elder  and  Einhorn,  is  a  hydro- 
chloride /?-aminobenzoyl-diethylamino-ethanol.  It  occurs  as 
thin  colorless  needles;  melts  at  156°  C,  soluble  in  one  part  water 
and  thirty  parts  alcohol.  It  is  seven  times  less  toxic  than  cocaine, 
and  three  times  less  toxic  than  stovaine.  It  can  be  steriHzed  by 
boiHng,  and  is  used  in  1/2  to  2%  solution  often  with  adrenahn 
I   1000.     (Mod.  Mat.  Med.,  page  275.) 

Novocaine,  if  intended  to  represent  a  solution  which  is  iso- 
tonic with  the  blood  corpuscles,  must  be  dissolved  in  a  0.92 
per  cent,  sodium  chloride  solution.  (Dental  Cosmos,  1910,  page 
605.) 

Oil  of  Cloves,  oil  of  Gaultheria,  and  other  essential  oils  may 
be  detected  by  the  same  process  of  fractional  evaporation  as 
suggested  for  menthol.  In  testing  for  the  presence  of  any  sub- 
stance by  its  odor,  it  is  usually  necessary  to  make  a  comparative 
test  on  known  samples  using  the  same  methods. 

Orthoform,  C6H30H(NH2)COOCH3,  methylpara-amino-meta- 
oxybenzoate,  used  as  an  anesthetic  and  antiseptic,  is  without 
odor,  color,  or  taste,  is  sUghtly  soluble  in  water,  and  easily  soluble 
in  alcohol  or  ether. 

Phenol.  —  CarboHc  acid,  CeHsOH,  obtained  from  the  de- 
structive distillation  of  coal-tar.  A  Hght  oily  Uquid  of  specific 
gravity  of  0.94-0.99.  Carbolic  acid  is  usually  obtained  as  a 
white  crystalline  mass  soluble  in  twenty  parts  of  water.  The 
pure  acid  turns  pink  with  age,  but  does  not  suffer  deterioration  on 
account  of  this  change  of  color.  The  addition  of  from  five  to 
eight  per  cent,  of  water  will  cause  liquefaction  of  the  crystals  and 
the  preparation  becomes  permanently  liquid.  It  is  easily  soluble 
in  glycerol  and  strong  solutions  may  thus  be  prepared.  Car- 
boHc acid  is  sometimes  added  to  local  anesthetics  with  the  in- 
tent of  rendering  the  solution  sterile,  but  as  shown  by  Dr. 
Endehnan  (Dental  Cosmos,  Vol.  45,  page  44)  it  would  be  neces- 


184  MICROCHEMICAL  ANALYSIS 

sary,  in  order  to  prevent  the  development  of  micro-organisms,  to 
add  the  acid  in  proportion  that  would  render  the  solution  unfit 
for  hypodermic  purposes. 

Tests.  —  Phenol  may  be  detected  in  the  majority  of  prepara- 
tions by  the  addition  of  bromine-water,  which  gives  white  crys- 
tals of  tribromphenol  (see  Plate  III,  Fig.  5).     See  also  Exp.  145. 

Phenol  Compound.  —  Dr.  Buckley's  formula  for  treatment  of 
root  canals  —  menthol  1.3  grams,  thymol  2.6  grams,  and  phenol 
12  c.c. 

Potassium  Hydroxide,  KOH,  gives  an  alkaline  reaction  to 
Htmus  paper  and  may  be  detected  by  the  ordinary  methods  of 
inorganic  analysis. 

Rhigolene  is  a  light  inflammable  liquid  obtained  from  petro- 
leum, boiling  at  about  18°  C,  used  as  a  spray  for  the  production 
of  low  temperature,  similarly  to  methyl  or  ethyl  chloride.  It 
is  readily  inflammable  and  the  vapor,  mixed  with  certain  pro- 
portions of  air,  is  explosive.     It  should  be  kept  in  a  cool  place. 

Ringer's  Solution,  which  is  used  as  a  solvent  for  Novocaine 
and  other  anesthetics  has  the  formula: 

Sodium  Chloride 0.50 

Calcium  Chloride 0.04 

Potassium  Chloride 0.02 

Distilled  water 100.00 

Saccharin.  —  Saccharin  is  official  in  the  ninth  revision  of  the 
Pharmacopoeia  as  benzosulphinidum.  It  is  a  derivative  of 
toluene  having  a  formula  of  C6H4COSO2NH,  being  benzoyl- 
sulphonimide.  It  is  a  white  crystalline  powder  melting  at  219° 
to  222°  C. 

It  is  said  to  be  at  least  three  hundred  times  sweeter  than 
cane  sugar  and  is  used  in  mouth-washes,  tooth-paste,  etc.,  as. a 
flavor  and  an  antiseptic. 

Test.  —  Add  a  few  drops  of  potassium  hydroxide  solution 
to  a  Uttle  saccharin;    heat  for  a  few  minutes.     Acidify  with 


LOCAL  ANESTHETICS  AND  ANTISEPTICS  185 

hydrochloric  acid;  add  a  few  drops  of  ferric  chloride;  when  a 
reddish  brown  or  purplish  color  is  produced. 

Silver  Nitrate,  AgNOs,  crystallizes  in  colorless  plates  without 
water  of  crystallization;  used  as  an  antiseptic,  disinfectant,  or 
escharotic.  It  is  freely  soluble  in  water  and  may  be  detected  by 
the  ordinary  methods  of  qualitative  analysis  (page  20). 

Sodium  Chloride,  NaCl,  is  a  constituent  of  many  prepara- 
tions designed  to  be  used  hypodermically.  Experience  has 
proved  the  value  of  such  addition;  perhaps  the  reason  for  its 
desirability  is  given  by  Dr.  G.  Mahe,  of  Paris,  in  the  Dental 
Cosmos  for  September,  1903,  in  the  statement  that  sodium 
chloride  added  in  excess  to  a  toxic  substance  diminishes  its 
toxicity  by  one-half,  and  this  has  been  demonstrated  particu- 
larly with  cocaine. 

Sodium  Perborate,  a  powder  having  the  composition 
NaB03.4  H2O,  which  will  furnish  10%  of  available  oxygen  and 
produce  H2O2  with  water;  very  stable  and  recommended  as  a 
bleach-powder. 

Sodium  perborate  may  be  made  by  thoroughly  mixing 
sodium  peroxide  (Na202)  with  crystallized  boric  acid  and  stir- 
ring the  mixture  gradually  into  cold  water.  The  proportions 
recommended  by  V.  E.  Miegeville  in  the  Dental  Cosmos  for 
1905,  page  1 38 1,  are  78  grams  of  the  sodium  peroxide,  248  grams 
of  the  boric  acid,  and  two  liters  of  water.  The  sodium  perborate 
is  formed  spontaneously  and  separates  from  the  solution  as  a 
white  crystalline  powder.  Its  solubility  is  increased  by  addition 
of  weak  organic  acids,  citric  or  tartaric. 

Sodium  Peroxide,  Na202.  —  A  white  powder  easily  soluble 
in  water,  usually  with  evolution  of  more  or  less  oxygen  and  forma- 
tion of  hydrogen  dioxide.        ^ 

Somnof orm.  —  A  general  anesthetic  administered  in  manner 
similar  to  chloroform;  introduced  by  Dr.  Rolland,  of  Bordeaux; 
consists  of  60%  ethyl  chloride,  35%  ethyl  bromide,  and  5% 
methyl  bromide.     (Dental  Cosmos,  Vol.  XL VII,  page  236.) 


l86  MICROCHEMICAL  ANALYSIS 

Stovaine.  —  Benzoylethyldimethyl-aminopropanol  hydrochlo- 
ride, C14H21O2N.HCI,  closely  related  to  alypin,  small  shining 
scales  freely  soluble  in  alcohol  or  water.  Incompatible  with 
alkalies  and  all  alkaloidal  reagents.  Can  be  sterilized  by  boil- 
ing.    (Mod.  Mat.  Med.,  2nd  edition.) 

It  melts  at  175°  C,  is  very  soluble  in  water,  and  gives  reaction 
similar  to  cocaine,  which  is  also  a  benzoyl  derivative.  (U.  S.  D., 
page  1 66 1.) 

It  is  less  powerful  than  cocaine  and  physiologically  incom- 
patible with  adrenalin.     (Dental  Cosmos,  1905,  page  146.) 

Test.  —  Stovaine  gives  rather  irregular  but  characteristic 
crystals  with  platinic  chloride.     (Plate  IV,  Fig.  4.) 

Suprarenal  Glands.  —  The  official  preparation  consists  of 
dried  glands  obtained  only  from  animals  used  for  food  by  man, 
and  which  must  contain  not  less  than  0.4%  nor  more  than  0.6% 
of  epinephrine. 

Tannic  Acid,  or  tannin,  sometimes  called  gallotannic  acid, 
is  an  astringent  organic  acid  obtained  from  nutgalls.  It  may 
be  obtained  as  crystals  carrying  two  molecules  of  water, 
HC14H9O9.2  HoO.  Tannic  acid  is  a  white  or  slightly  yellowish 
powder  soluble  in  about  one  part  of  water  or  0.6  part  alcohol. 
It  is  used  as  an  alkaloidal  precipitate,  also  in  astringent  washes. 
It  may  be  detected  by  the  addition  of  ferric  solutions  which 
form  with  it  a  black  tannate  of  iron  of  the  nature  of  ink. 

Thymol,  CeHafCHslfOHjfCaH:)  1:3:4-  This  is  a  phenol 
which  occurs  in  volatile  oils  of  thymus  vulgaris  (Linne).  Melts 
at  44°  C;  sparingly  soluble  in  water,  easily  in  alcohol  and 
ether. 

Tests.  —  It  may  usually  be  detected  by  its  odor  or  by  dis- 
solving a  small  crystal  in  i  c.c.  of  glacial  acetic  acid,  when,  if 
six  drops  of  sulphuric  acid  and  one  drop  of  nitric  acid  be  added; 
the  Hquid  ^\dll  assume  a  deep  bluish-green  color.     (U.  S.  D.) 

Thymol  iodide,  diiododithymol,  (C6Ho.CH3.C3H70I)2,  a  valua- 
ble antiseptic  containing  forty  three  per  cent,  of  iodine.     It  is 


WCAL  ANESTHETICS  AND  ANTISEPTICS  187 

brown  powder  insoluble  in  water,  slightly  soluble  in  alcohol, 
easily  soluble  in  chloroform  or  ether. 

Thymophen,  a  mixture  of  equal  parts  of  thymol  and  phenol. 

Thyroids.  —  The  dried,  powdered,  thyroid  glands  of  animals 
used  for  food  by  man,  freed  from  connective  tissue  and  fat, 
containing  not  less  than  0.17%  or  more  than  0.23%  of  iodine, 
constitutes  the  official  preparation  used  as  a  remedy  in  myxedema 
and  other  cases  of  perverted  metabolism. 

Trichloracetic  Acid  occurs  as  deliquescent  crystals,  readily 
soluble  in  water.  Distils  at  195°  C.  and  is  a  powerful  caustic. 
Dilute  solutions  are  recommended  for  treatment  of  pyorrhea. 

Tropa-cocaine  is  an  alkaloid  originally  isolated  by  Giesel 
from  the  leaves  of  the  small-leaved  coca-plant  of  Java  and  intro- 
duced by  Arthur  P.  Chadbourne,  Harvard  Medical  School. 
Used  hypodermically  in  normal  salt  solution.  It  is  probably 
superior  to  cocaine,  but  rather  more  expensive.  It  is  obtained 
as  an  oil  which,  when  quite  dry,  soUdifies  in  radiating  crystals, 
melting  at  49°  C. .   It  is  easily  soluble  in  alcohol. 

A  number  of  commercial  mouth-washes  and  local  anesthetics 
will  be  given  to  the  class  for  identification,  the  object  being  to 
familiarize  the  student  with  the  more  easily  made  tests  for  the 
principal  ingredients  of  these  preparations.  Complete  analysis 
will  rarely  be  attempted.  The  following  table,  taken  from  the 
Druggist's  Circular  of  June,  1910,  may  be  helpful. 


i88 


MICROCHEMICAL  ANALYSIS 


DIFFERENTIATION  OF  COCAINE  AND   ITS   SUBSTITUTES. 


Iodine  potassium 
iodide. 

Bromine  water. 

Sodium  hydroxide. 

Potassium  per- 
manganate. 

Eucaine  —  a. 

Yellow-maroon 

Yellow  precipitate. 

White  precipitate. 

Violet  precipitate. 

precipitate, 

soluble  on  heat- 

insoluble in  ex- 

blackening 

soluble  on 

ing. 

cess  and  on  boil- 

quickly. 

boiling. 

ing. 

Eucaine  —  b. 

Deep-red  pre- 

Yellow precipitate. 

White  precipitate. 

N'o  precipitate 

cipitate,  solu- 

slightly soluble 

insoluble  in  ex- 

immediately; 

ble  on  boiling. 

on  heating,  re- 

cess  and  on 

color  persists 

precipitated 

boiling. 

for  a  day. 

white  on  boiling. 

Cocaine 

Yellow-maroon 

Yellow  precipitate. 

White  precipitate. 

Violet  precipitate. 

precipitate. 

soluble  on  heat- 

insoluble in  ex- 

color persists 

soluble  on 

ing. 

cess  and  on 

for  one  hour. 

boiling. 

boiling. 

then  deposits 
MnOs. 
Violet  precipitate, 

Novocaine 

Deep-red  pre- 

Yellow precipitate, 

White  precipitate. 

cipitate,  solu- 

soluble on  heat- 

insoluble in  ex- 

blackening 

ble  on  boiling. 

ing. 

cess  and  on  boil- 

quickly 

Stovaine 

Deeph-red  pre- 

Yellow precipitate. 

ing. 
White  precipitate, 

Violet  precipitate, 

cipitate,  solu- 

soluble on  heat- 

insoluble in  ex- 

blackening al- 

ble on  boiling. 

ing. 

cess;  aromatic 
odor  on  boiling. 

most  immedi- 
ately. 

Nirvanin 

Deep-red  pre- 

Yellow precipitate, 

Precipitate,  very 

Precipitate,  first 

cipitate,  solu- 

soluble on  heat- 

soluble in  excess 

maroon,  then 

ble  on  boiling. 

ing,  but  the 
liquid  becomes 
red  and  gives  an 
agreeable  fruity 
odor. 

of  the  reagent. 

brown. 

Alypin 

Yellow-maroon 

Yellow  precipitate. 

White  precipitate. 

Bluish-violet  pre- 

precipitate, in- 

soluble on  gentle 

insoluble  in  ex- 

cipitate, slowly 

soluble  on 

heating. 

cess  and  on  boil- 

blackening. 

boiling;  orange- 

ing. 

red  deposit. 

CHAPTER  XX. 
TEETH   AND   TARTAR. 

The  chemical  examination  of  teeth  and  tartar,  while  coming 
more  properly  under  the  head  of  physiological  chemistry,  will 
be  considered  in  part  in  this  place,  as  the  tests  made,  especially 
on  tartar,  are  practically  all  microchemical.  The  composition 
of  the  cement  is  practically  that  of  true  bone,  the  dentine  and 
enamel  differing  principally  in  the  proportion  of  organic  matter 
which  they  contain.  In  all  of  these  the  presence  of  lime,  phos- 
phoric acid,  carbonic  acid,  and  traces  of  magnesium  and  calcium 
fluoride  may  be  demonstrated.  The  tartar  contains  a  greater 
proportion  of  carbonic  acid,  less  calcium  phosphate,  and  much 
less  organic  matter  than  the  teeth,  taken  as  a  whole,  or  than 
dentine,  but  about  the  same  as  enamel.  According  to  Berzehus, 
sodium  chloride  and  sodium  carbonate  may  also  be  found. 

The  composition  of  the  different  parts  of  the  tooth  sub- 
stance has  been  given  as  follows: 

?fa«en  ^^^^-  Ca3(P04)2.  MgHPOi.  CaCOj. 

Dentine 23.2  76.8         70.3  4.3         2.2 

Cement 32.9  67.1         60.7  1.2         2.9 

Enamel 3.1  96  •  9         9°  •  5  traces       2 .  2 

Also  traces  of  magnesium  carbonate,  calcium  sulphate,  fluorides, 
and  chlorides.  x\n  increase  in  the  percentage  of  calcium  phos- 
phate of  fluoride  increases  the  hardness  of  the  tooth,  while  an 
increase  of  calcium  carbonate  decreases  the  hardness. 

Potassium  sulphocyanate,  ferric  phosphate,  sulphites,  and 
uric  acid  have  been  found  in  tartar,  as  additional  chemical 
constituents,   while   after   the   solution   of   the  mineral  matter 


IQO  MICROCHEMICAL  ANALYSIS 

the  presence  of  epithelium  cells,  mucus,  and  the  leptothrix  may 
be  demonstrated  by  the  microscope. 

According  to  Vergness,  Du  tartre  dentaire,  quoted  by  Gamgee. 
the  tartar  from  incisor  teeth  and  that  from  molars  show  decided 
difference  in  their  content  of  iron  and  calcium  phosphates,  the 
analysis  being  as  follows: 

Tartar  of  Incisors.  Tartar  of  Molars. 

Calcium  phosphate 63 .  88-62  .56  55 . 1 1-62 . 1 2 

Calcium  carbonate 8.48-  8.12  7  36-  8. or 

Phosphate  of  iron 2,72-  0.82  12.74-  4  01 

Silica o.  21-  o.  21  0.37-0.38 

Alkaline  salts o.  21-  o.  14  0.37-0.31 

Organic  matter 24.99-27.98  24.40-24.01 


Deposition  of  Tartar  Under  Various  Systemic 
Conditions. 

The  presence  of  oxalates  and  urates  have  been  reported 
in  the  black  tartar  from  pyorrhea  cases.  The  deficient  oxidation 
and  high  acidity  usually  occurring  in  such  cases  is  conducive  to 
the  production  of  large  amounts  of  oxalic  or  uric  acids  in  the  sys- 
tem, not  necessarily  on  the  teeth,  whether  these  substances  have 
etiological  relations  to  pyorrhea  or  not. 

The  formation  of  ordinary  hard  tartar  consisting  princi- 
pally of  phosphate  and  carbonate  of  calcium  is  accounted  for  by 
Dr.  Percy  G.  Howe*  as  follows:  An  excess  of  calcium  salts 
in  the  blood  must  be  granted  as  one  of  the  causes  of  calcification. 
These  calcium  salts  are  held  in  solution  by  two  distinct  factors: 
first,  the  excess  of  carbon  dioxide;  and  second,  by  the  presence 
of  colloidal  substances  in  suspension.  This  accounts  for  the 
fact  that  the  loss  of  carbon  dioxide  does  not  universally  precipi- 
tate the  lime  salts.  Barille  holds  that  calcium  phosphate  occurs 
in  the  blood  as  an  unstable  carbon  phosphate  which  tends  to 
decompose  into  calcium  acid  phosphate  and  bicarbonate,  and  that 

*  Dental  Cosmos,  1915,  page  307. 


TEETH  AND   TARTAR  191 

in  saliva  we  find  both  these  salts  held  in  solution  by  carbon 
dioxide  as  follows: 

Ca3(P04)2  +  4H2CO3  =  HoO  +  P208Ca2H2.2  C03(C03H)2Ca. 

Upon  the  escape  of  the  carbon  dioxide,  the  calcium  precipitates 
as  the  tri-metallic  phosphate  if  the  solution  is  alkaline,  and  as 
dicalcic  phosphates  if  the  solution  is  acid;  and,  of  course,  the 
loss  of  carbon  dioxide  will  at  the  same  time  result  in  the  pre- 
cipitation of  the  neutral  carbonate  (CaCOs). 

That  the  general  systemic  condition  is  also  a  factor  in  the 
deposition  of  tartar  is  indicated  by  the  experience  of  Dr.  Wright 
of  the  Harvard  Dental  School,  who  has  watched  for  a  succession 
of  years  the  fairly  uniform  increase  in  tartar  deposits  from  Oc- 
tober to  June,  and  has  found  the  vacation  period  marked  by 
smaller  amounts  of  deposit. 

Lactic  and  other  organic  acids  have  been  found  in  minute 
quantities  in  tartar,  but  these  as  well  as  the  qualitative  tests  for 
urates  will  be  considered  more  in  detail  under  the  Chemistry 
of  Saliva. 

Analysis  of  Teeth  and  Tartar. 

The  substance  for  analysis  should  be  reduced  to  a  moder- 
ately fine  powder  by  crushing  in  a  mortar  and  a  fair  sample  of 
the  whole  taken  for  each  test. 

Moisture  may  be  detected  by  the  closed-tube  test  (page  105) 
and  ma}'  be  determined  by  accurately  weighing  out  one  gram 
of  the  substance  in  a  counterpoised  platinum  dish  or  crucible 
and  dr^dng  at  100°  C.  to  constant  weight. 

Inorganic  matter  may  be  determined  by  careful  ignition  of 
dried  siibstance;  raise  the  temperature  slowly  till  full  red  heat 
is  reached;   cool  in  a  desiccator  -and  weigh. 

Organic  niatter  may  be  ascertained  by  ditierence. 

Lactates  and  other  organic  acids  may  be  detected  by  careful 
crystalUzation  and  examination  with  the  micropolariscope. 


192  MICROCHEMICAL  ANALYSIS 

The  several  inorganic  constituents  may  be  demonstrated  as 
follows : 

Phosphoric  Acid.  —  Dissolve  a  little  of  the  powdered  sub- 
stance in  dilute  nitric  acid;  then  to  a  few  drops  of  the  clear 
solution  add  an  excess  of  ammonium  molybdate  in  nitric  acid. 
A  yellow  crystalline  precipitate  of  ammonium  phosphomolybdate 
will  separate.  Avoid  heating  above  60°  C,  as  the  ammonium 
molybdate  may  decompose  and  precipitate  a  yellow  oxide  of 
molybdenum. 

Carbonic  Acid  may  be  detected  by  Hberation  of  carbon 
dioxide  and  passing  the  gas  into  lime-water  as  described  on  page 
93  or  with  closed  tube  and  drop  of  baryta-water,  page  105. 

Chlorine  may  be  detected  in  the  dilute  nitric  acid  solution  by 
the  usual  silver  nitrate  test. 

Calcium  and  Magnesium  may  be  separated  and  identified 
by  the  usual  methods  of  analysis  in  the  presence  of  phosphates. 

Test  for  calcium  and  magnesium  as  follows:  Add  to  the 
hydrochloric  acid  solution  an  excess  of  ammonia;  calcium  phos- 
phate and  magnesium  phosphate  are  precipitated,  white.  Filter 
and  to  the  filtrate  add  ammonium  oxalate;  a  white  precipitate 
shows  lime,  not  as  phosphate.  Wash  the  precipitate  produced 
by  ammonium  hydroxide,  dissolve  in  dilute  hydrochloric  acid, 
and  add  ferric  chloride  carefully  till  a  drop  of  the  solution  gives, 
when  mixed  with  a  drop  of  ammonium  hydroxide,  a  yellowish 
precipitate.  Nearly  neutralize  with  sodium  carbonate  and  add 
barium  carbonate,  which  precipitates  ferric  phosphate.  Filter, 
heat  the  filtrate,  precipitate  the  barium  with  dilute  sulphuric 
acid,  and  filter  again.  From  the  filtrate  calcium  is  precipitated 
as  white  calcium  oxalate  by  making  it  alkaline  with  ammonium 
hydroxide  and  adding  ammonium  oxalate  as  long  as  a  precipitate 
is  formed.  Filter  and  add  to  the  filtrate  sodium  phosphate,  which 
precipitates  magnesium  as  ammonio-magnesium  phosphate,  white. 

Laboratory  Exercises  may  consist  of  the  examination 
by  microchemical  methods  of  one  or  more  samples  of  tartar. 


PART   V. 

ORGANIC  CHEMISTRY. 

CHAPTER  XXI. 

THE  HYDROCARBONS  AND  SUBSTITUTION  PRODUCTS. 

Our  work  up  to  this  point  has  been  confined  to  inorganic 
chemistry  excepting  a  few  microchemical  tests  for  organic 
substances. 

We  are  now  to  consider  briefly  the  organic  compounds  which 
will  serve  as  a  basis  for  the  intelHgent  study  of  physiological 
chemistry,  and  also  some  which  are  of  pecuHar  interest  in  den- 
tistry. 

We  shall  touch  but  lightly  on  some  of  the  subdivisions  of  the 
subject  and  take  up  a  Httle  organic  chemistry  proper,  a  little 
physiological  chemistry,  a  Httle  pathological  chemistry,  and 
from  it  all  pick  out  such  facts  as  may  help  us  to  a  better  under- 
standing of  the  problems  of  dentistry. 

As  in  many  other  departments  of  science,  absolute  rules  for 
classification  are  impracticable;  yet  we  may  consider  in  a 
general  way  that  the  organic  compounds  are  those  containing 
carbon  as  a  molecular  constituent.  The  old  conception  that  the 
organic  compound  must  have  been  produced  by  a  vital  process 
of  some  sort  (animal  or  vegetable)  is  of  Httle  value  unless  we  con- 
fine our  thought  to  substances  found  in  nature  only. 

The  compounds  of  carbon  are  practically  innumerable  and 
very  widely  distributed,  ^constituting  the  great  bulk  (aside  from 
water)  of  all  vegetable  or  animal  substances. 

The  carbon  compounds  contain  the  elements  of  carbon  and 
hydrogen,  and  when  these  two  only  are  present  they  are  hydro- 

193 


194  ORGANIC  CHEMISTRY 

carbons.  They  more  frequently  contain  carbon,  hydrogen,  and 
oxygen,  and  when  the  hydrogen  and  oxygen  are  present  in  the 
proportions  in  which  they  occur  in  water,  the  compound  is  a 
carbohydrate  (with  exceptions). 

In  the  chemistry  of  the  animal  body  the  majority  of  sub- 
stances which  we  meet  contain  carbon,  hydrogen,  oxygen,  and 
nitrogen  and  often  in  addition  sulphur  or  phosphorus.  Many 
other  elements,  notably  the  halogens,  and  often  the  metals,  may 
be  found  in  organic  compounds. 

The  question  of  its  composition  is  then  the  first  one  pre- 
senting itself  in  the  consideration  of  an  organic  substance. 

The  analysis  of  organic  bodies  may  be  made  from  two  dis- 
tinct standpoints:  first,  to  determine  the  various  substances 
which  may  be  separated  from  a  given  organized  body,  as  from 
some  part  of  a  plant;  secondly,  to  determine  the  constituent 
elements  of  one  of  the  substances  so  separated. 

As  an  example  of  the  first  sort  of  analysis,  we  may  find  in  a 
potato  a  certain  basic  principle  (alkaloid),  more  or  less  water, 
and  considerable  starch.  These  may  be  called  proximate  prin- 
ciples, and  the  separation  of  them  would  be  proximate  analysis, 
while  the  second  sort  of  analysis  determines  the  composition  of 
the  starch  molecule  and  is  known  as  ultimate  analysis. 

Qualitative  Tests. 

Carbon.  —  The  presence  of  this  element  may  be  shown  by 
the  "  carbonization  "  obtained  in  the  preliminary  test,  as  given 
on  page  104. 

Hydrogen  shows  itself  by  the  production  of  moisture  in 
these  same  tests. 

Nitrogen  may  or  may  not  be  indicated  by  the  preliminary 
test.  It  may  be  detected  with  certainty  by  either  of  the  fol- 
lowing methods : 

(a)  Conversion  into  a  cyanogen  compound. 


THE  HYDROCARBONS  AND  SUBSTITUTION  PRODUCTS      195 

A  small  piece  of  thoroughly  dried  albumin  together  with 
a  Httle  metallic  potassium  is  placed  in  a  matrass,  such  as  is 
described  on  page  34,  and  heated  to  redness  for  a  few  minutes. 
(Metallic  sodium  will  work  as  well  in  most  cases.)  An  alkali 
cyanide,  which  may  be  dissolved  in  water  after  breaking  the 
tube,  is  formed,  and  by  addition  of  a  little  yellow  ammonium 
sulphide  and  evaporation  to  dryness  on  a  water-bath  will  be 
changed  to  sulphocyanate,  NH4CNS.  If  the  dry  residue  is  taken 
up  with  dilute  hydrochloric  acid,  filtered,  and  tested  with  a 
drop  of  ferric  chloride  solution,  the  presence  of  the  sulphocyanate 
is  at  once  shown  by  the  red  color  produced. 

(b)    Conversion  into  free  ammonia. 

Almost  any  nitrogenous  substance  may  be  made  to  evolve 
ammonia-gas  by  simply  heating  in  a  test-tube  with  several  times 
its  bulk  of  soda-hme.  Test  for  ammonia  by  moistened  red  Utmus 
paper  or  by  odor.  (This  test  is  known  as  that  of  Wohler,  also 
of  Will  and  Varrentrap.) 

The  KjeldahL  or  moist  combustion  process  is  much  employed 
as  a  quantitative  method  but  may  be  used  quaHtatively  as 
follows:  The  substance  is  heated  in  an  ignition- tube  with  con- 
centrated sulphuric  acid  till  a  clear  (not  necessarily  color- 
less) solution  is  obtained.  The  mixture  is  cooled,  diluted  with 
water,  an  excess  of  caustic  soda  added,  and  heat  applied  when 
ammonia  is  evolved,  which  may  be  detected  by  litmus  paper  or 
by  odor. 

Sulphur  and  Phosphorus  are  first  completely  oxidized  either 
by  fusion  of  the  substance  with  alkah  nitrate  and  carbonate 
or  by  treatment  in  the  wet  way  with  fuming  nitric  acid  or  mix- 
ture of  potassium  chlorate  and  hydrochloric  acid.  The  result- 
ing sulphate  ov  phosphate^  is  detected  by  the  usual  qualitative 
methods  (page  95). 

A  sulphur  test  may  also  be  made  by  heating  the  substance 
with  a  little  concentrated  sodium  hydroxide  in  the  test-tube. 
A  little  sodium  sulphide,  which  may  be  detected  by  dropping  onto 


196  ORGANIC   CHEMISTRY 

a  bright  silver  coin  or  by  testing  with  lead  acetate  solution,  will 
thus  be  formed. 

Halogens.  —  Chlorine,  bromine,  and  iodine  cannot  be  de- 
tected in  organic  combinations  by  the  ordinary  qualitative  test 
with  silver  nitrate  and  dilute  nitric  acid,  but  must  first  be  con- 
verted into  corresponding  inorganic  haloid  salts.  This  may  be 
done  by  heating  the  organic  substance  strongly  with  pure  lime, 
when  calcium  chloride,  bromide,  etc.,  which  may  be  dissolved  in 
water  and  tested  in  the  usual  way,  will  be  formed.  (See  pages 
96  and  97.) 

A  test  for  chlorine  or  iodine  may  also  be  made  by  heating 
with  copper  oxide  on  a  platinum  wire  in  the  Bunsen  flame,  chlo- 
rine giving  first  a  blue  then  a  green  color  to  the  flame.  Iodine 
gives  a  green  only  (Beilstein). 

Test  for  presence  of  C,  H,  and  S  in  dried  albumin. 

Test  for  S  by  the  caustic  soda  test. 

Test  for  P  in  casein  precipitated  from  milk. 

Test  a  few  drops  of  chloroform  for  the  presence  of  chlorine. 

The  Hydrocarbons. 

The  hydrocarbons  are  organic  compounds  of  carbon  and 
hydrogen  only.  The  simplest  of  these  is  marsh-gas  or  methane 
(CH4).  The  molecule  of  this  substance  consists  of  a  single 
carbon  atom  with  each  of  its  four  points  of  atomic  attraction 
(valence)  satisfied  by  an  atom  of  hydrogen. 

H  H 

/     \ 
H  H 

If  one  of  these  four  atoms  of  hydrogen  is  replaced  by  a  chlo- 
rine atom,  for  instance,  we  have  a  substitution  product.  Its  for- 
mula will  be  CH3CI,  its  name  monochlormethane  or  methyl 
chloride.  If  two  molecules  of  methyl  chloride  are  brought  to- 
gether and  the  chlorine  removed  by  metallic  sodium  the  residual 


THE  HYDROCARBONS  AND  SUBSTITUTION   PRODUCTS      197 

molecules  (methyl  radicals)  will  unite,  forming  a  new  hydrocar- 
bon, as  follows: 

2  CH3CI  +  Nao  =  2  NaCl  +  GHg  (ethane). 

By  a  similar  reaction  we  may  form  the  third  member  of 
the  series,  CsHg  (propane),  from  ethyl  chloride  (C2H6CI)  and 
sodium;  the  fourth  member,  butane,  C4H10,  from  propyl  chloride, 
etc.  A  tabulated  list  of  the  first  five  compounds  of  this  series 
will  plainly  show  their  chemical  relationship. 

CH4,  methane  or  methyl  hydride  (CH3H). 
C2H6,  ethane  or  ethyl  hydride  (C2H5H). 
C3H8,  propane  or  propyl  hydride  (C3H7H). 
C4H10,  butane  or  butyl  hydride  (C4H9H). 
C5H12,  pentane  or  amyl  hydride  (C5H11H). 

Note  that  the  various  members  of  this  series  differ  from  one 
another  by  CH2;  that  is,  each  higher  compound  contains  one 
carbon  atom  and  two  hydrogen  atoms  more  than  its  predecessor. 
This  holds  true  through  the  series,  and  the  compounds  of  this 
or  any  such  series  are  termed  homologues  and  the  series  ho- 
mologous series.  Note  further  that  any  member  of  this  series 
(which  is  known  as  the  paraffin  series)  may  be  represented  by 
the  general  formula  C„H2„+2.  This  Hkewise  holds  true  through- 
out the  series,  and  a  compound  having  sixty  carbon  atoms  will 
have  a  formula  of  CeoHm.  The  first  four  hydrocarbons  of  this 
series  are  gaseous  at  ordinary  temperatures;  from  C5H12  to 
about  C16H34  the  hydrocarbons  are  Hquid;  from  C16H34  (melt- 
ing at  about  18°)  up  they  are  soHds. 

Isomers.  —  When  two  or  more  compounds  are  of  exactly 
the  same  molecular  composition,  or  when  two  compounds  have 
the  same  percentage  composition  the  one  being  a  multiple  of  the 
other,  the  compounds  are  said  to  be  isomers  or  isomeric  com- 
pounds. 

The  isomerism  of  the  first  class  is  said  to  be  metameric  when 


iqS  organic  chemistry 

the  atoms  of  the  several  compounds  are  not  only  the  same  in 
kind,  but  also  the  same  in  the  number  of  each  kind.  For  ex- 
ample, Ci2H>20ii  is  the  formula  for  cane  sugar;  C12H22O11  is  also 
the  formula  for  milk  sugar,  and  these  two  compounds  have 
decidedly  dififerent  properties,  the  difference  being  dependent 
upon  the  arrangement  or  relationship  of  the  atoms  in  the  mole- 
cule. Another  example  illustrating  this  difference  may  be 
found  in  the  graphic  formula  for  normal  and  isobutane  given 
below. 


H 
H 
/ 


H 
H    H    H    H  \ 

I       I       I       I  H  /C 

H-C-C-C-C-H  I  / 

I      I      I       I  H-C-C\  „ 

H    H    H    H  I        I   \    / 

H     H        C-H 


Note  that  each  molecule  has  an  empirical  formula  of  C4H10; 
the  normal  compound  may  be  represented  as  CH3.(CH2)2.CH3, 
the  iso-compound  as  CH3.CH.(CH3)2.  These  will  be  found  to 
have  quite  different  physical  and  chemical  properties. 

The  isomerism  of  the  second  class  is  called  polymeric  and  one 
substance  is  the  polymer  of  another  when  the  molecules  are  of 
the  same  percentage  composition  but  of  different  molecular 
weights,  for  example,  CH2O  is  gaseous  formaldehyde,  (CH20)3  is 
its  polymer  or  polymeric  form,  known  as  paraform,  a  white 
crystalline  solid. 

The  hydrocarbons  of  the  paraffin,  series  are  known  as  straight 
chain  or  aliphatic  hydrocarbons,  their  graphic  formulae  consist- 

I  I  I  I 
ing  of  "  chains  "  of  carbon  atoms,  as  butane,  — C  — C  — C  — C  — , 

I  I  I  I 
in  distinction  from  the  closed-chain  or  cyclic  compounds  as  repre- 


THE  HYDROCARBONS  AND  SUBSTITUTION   PRODUCTS      199 


sented  by  the  "  benzene-ring  "  (page 
244)  carbon  nucleus  with  the  carbon 
atoms  united  in  a  continuous  dosed 
chain  or  "  cycle." 

The  paraffins  are  called  saturated 
hydrocarbons  because  they  are  inca- 
pable of  forming  addilion  products  by 
absorption  of  chlorine,  for  instance, 
without  first  gixang  off  an  equivalent 
number  of  atoms  of  hydrogen.  This 
is  because  of  the  complete  "  satura- 
tion "  or  union  of  every  carbon 
"  bond "  with  some  other  atom.* 
Paraffin  wax  and  mineral  oil  are  mix- 
tures of  saturated  hydrocarbons  and 
resist  chemical  action  even  of  strong 
nitric  acid  or  sulphuric  acid. 

The  name  paraffin  is  derived  from 
the  two  Latin  words  parvus,  httle,  and 
affinitas,  affinity. 

The  natural  sources  of  hydrocar- 
bons of  the  paraffin  series  are  natural 
gas  and  crude  petroleum,  or  rock  oil. 
Many  of  these  hydrocarbons  exist  as 
such  in  the  petroleum,  and  some  un- 
doubtedly are  produced  by  the  heat 
used  to  effect  a  separation  of  the  va- 
rious compounds.  This  separation 
may  be  efi'ected  by  distilling  the  oil 
in  an  apparatus  similar  to  that  pic- 
tured in  Fig.   17,   and  Is  known  as 

*  Notice  that  while  addition  products  of 
saturated  hydrocarbon  cannot  be  formed,  sub- 
stitution products  are  easily  possible.  See 
page  203. 


Fig.  17. 


200  ORGANIC  CHEMISTRY 

fractional  distillation,  the  different  hydrocarbons  passing  over  at 
different  temperatures.  Separation  by  tliis  method,  however,  is 
by  no  means  complete,  and  the  resulting  products  are  them- 
selves mixtures  of  hydrocarbons,  and  are  distinguished  by  physi- 
cal properties  rather  than  by  chemical  composition. 

When  crude  petroleum  is  thus  distilled,  the  following  products 
are  obtained:  first,  rhigoline,  which  comes  over  at  a  temperature 
of  20°  to  22°  C;  then  petroleum  ether  or  benzine  at  from  50° 
to  60°  C;  then  gasolene  or  naphtha  at  about  75°  C;  then  one 
or  two  unimportant  commercial  products,  and  kerosene  or  burn- 
ing oil  is  obtained  at  150°  to  250°  C.  Above  this,  we  may  obtain 
paraffin  oil  or  hght  lubricating  oils;  then  the  heavy  lubricating 
or  cylinder  oils,  and  from  the  residue  we  obtain  the  soHd  sub- 
stances known  as  vaseline  or  petroleum  jelly  and  paraffin  of 
various  degrees  of  hardness. 

The.  first  five  hydrocarbons  of  this  series  we  will  consider 
somewhat  in  detail,  not  only  because  they  are  important  and 
comparatively  common,  but  also  because  they  serve  as  types  of 
all  other  compounds  of  the  series,  and  reactions  which  we  study 
with  these  compounds  are,  as  a  rule,  general  typical  reactions 
which  may  be  produced  with  other  members  of  the  series. 

Methane,  CH4,  occurs  as  marsh  gas  in  stagnant  ponds  or 
pools  and  is  a  constituent  of  "  fire  damp  "  in  coal  mines.  It  is 
a  colorless  gas,  odorless  when  pure,  and  very  slightly  soluble 
in  water.  It  may  be  prepared  artificially  by  the  decomposi- 
tion of  anhydrous  sodium  acetate,  with  sodium  hydroxide  and 
lime.  See  reaction  on  page  382,  Exp.  63.  Methane  burns  in 
the  air  with  the  production  of  carbon  dioxide  and  water 
CH4  +  2  O2  =  CO2  +  2  H2O. 

Ethane,  C2H6,  the  second  member  of  the  series,  occurs  natur- 
ally in  a  solution  in  crude  petroleum,  and  can  be  artificially  pre- 
pared by  the  electrolytic  decomposition  of  a  saturated  solution 
of  potassium  acetate  as  follows: 

2  CH3COOK  =  C2H6  -f  2  CO2  +  K2. 


TUE   HYDROCARBONS  AND  SUBSTITUTION  PRODUCTS      20I 

The  free  potassium,  of  course,  decomposes  water,  liberating 
hydrogen  gas  which  collects  at  the  negative  pole,  and,  if  the 
solution  contains  sufficient  potassium  hydroxide,  the  carbon 
dioxide  will  be  dissolved,  allowing  ethane  to  collect  at  the  posi- 
tive pole. 

Ethane  may  also  be  made  from  a  haloid  derivative  of  marsh 
gas  by  the  action  of  metalHc  sodium;  that  is,  in  CH4  we  may 
replace  one  of  the  hydrogen  atoms  with  iodine,  forming  CH3I, 
methyl  iodide;  then  by  treatment  with  metallic  sodium,  the 
following  reaction  will  take  place: 

2  CH3I  +  2  Na  =  C2H6  +  2  Nal. 

Ethane  is  slightly  more  soluble  in  water  than  methane.  It 
may  be  condensed  to  a  liquid  at  a  pressure  of  forty-six  atmos- 
pheres. 

Propane,  CsHg,  also  occurs  in  petroleum,  and  can  be  made  by 
treating  a  mixture  of  ethyl  iodide  and  methyl  iodide  with  metallic 
sodium: 

C2H5I  +  CH3I  -f-  2  Na  =  C3H8  +  2  Nal. 

This  is  a  general  method  for  building  up  hydrocarbon  com- 
pounds. Propane  at  ordinary  atmospheric  pressure  is  condensed 
to  Hquid  at  17°  below  zero. 

Butane,  C4H10,  is  the  first  of  the  series  capable  of  existing  in 
two  forms,  isomers.  The  structural  formulas  of  these  two  com- 
pounds are  shown  in  the  illustration  of  the  term  isomer  on  page 
198.  This  compound  and  many  of  its  higher  homologues  are 
of  importance  only  in  relation  to  some  of  their  derivatives 
which  Tsdll  be  subsequently  studied. 

Unsaturated  Hydrocarbons, 
double-bonded  hydrocarbons. 

When  a  mixture  of  alcohol  and  strong  sulphuric  acid  is 
heated,  \\ath  the  acid   in    considerable  excess,  water  is  with- 


202  ORGANIC  CHEMISTRY 

drawn  from  the  molecule  of  alcohol,  and  a  gas  found  to  have  the 
formula  C2H4  is  produced.  (See  Exp.  64.)  The  name  of  this 
gas  is  ethylene;  it  occurs  in  coal  gas  and  in  traces  In  solution 
in  crude  petroleum.  It  is  the  first  of  a  series  of  hydrocarbons 
which  contain  double-bonded  carbon  atoms.  The  double  bond 
is  assumed  because  it  is  found  to  be  impossible  to  produce  a 
lower  compound  of  this  series,  such  as  CH2,  which  might  be 
called  methylene,  but  wliich  would  necessitate  a  bivalent  carbon 
atom;  also  because  the  hydrocarbons  of  this  series  are  capable 
of  formation  of  addition  products  as  well  as  of  substitution 
products. 

Note  that  the  formula  of  ethylene  does  not  conform  to  the 
general  formula  of  the  paraffins  (C„H2,j-[-2),  but  is  the  first  member 
of  the  new  series  of  "  unsaturated  "  hydrocarbons;  the  olefin  or 
ethylene  series  with  a  general  formula  of  C„H2„. 

The  hydrocarbons  of  this  series  take  their  names  from  corre- 
sponding members  of  the  parafiin  series,  with  "  ene  "  as  a  dis- 
tinguishing termination  —  ethylene,  C2H4,  propylene,  CsHc, 
butylene,  C4H8,  etc.  They  are  unimportant  in  dental  or  physio- 
logical chemistry.  Some  of  the  higher  oxygenated  compounds 
of  this  class  are,  however,  of  great  importance,  as  olein,  which 
is  a  constituent  of  vegetable  and  animal  fats  and  oils. 

TRIPLE-BONDED  HYDROCARBONS. 

A  third  series  of  the  straight  chain  hydrocarbons  is  the 
acetylene  series;  these  are  triple  bonded,  and  of  course  unsatu- 
rated, with  a  general  formula  of  C„H2„-2. 

The  only  members  of  this  series  of  special  interest  are,  first, 
acetylene,  H  — C  =  C— H,  (C2H2),  made  from  calcium  carbide 
and  water  (see  Exp.  67,  page  382).  It  is  poisonous,  combining 
directly  with  the  hemoglobin  of  the  blood,  has  a  disagreeable 
odor,  and  is  inflammable;  second,  allylene,  C3H4,  derivatives  of 
which  occur  in  onions,  garhc,  mustard-oil,  etc. 


THE  HYDROCARBONS  AND  SUBSTITUTION  PRODUCTS      203 

Haloid  Derivatives  of  the  Paraffins. 

Methane  furnishes  three  chlorine  substitution  products  which 
are  more  or  less  in  common  use:  first,  the  monochlor-methane,  or 
methyl  chloride;  second,  the  trichlor-methane  CHCI3  or  chloro- 
form, and  third,  the  tetrachloride  of  carbon  CCI4. 

Methyl  Chloride,  CH3CI,  may  be  made  from  methyl  alcohol, 
zinc  chloride,  and  hydrochloric  acid.  It  is  a  colorless  gas,  con- 
densing to  a  liquid  at  23°  C;  used  as  a  spray  in  producing  local 
anesthesia  (page  182);  also  as  a  constituent  of  anesthetics,  such 
as  anesthol,  somnoform,  etc. 

Dichlor-methane,  CH2CI2,  also  known  as  methylene  chloride, 
has  been  used  as  a  general  anesthetic  usually  mixed  in  more  or 
less  chloroform  and  alcohol.  Its  use  in  this  way  is  open  to 
criticism  because  of  its  poisonous  action,  affecting  the  heart. 

Chloroform,  CHCI3,  trichlorme thane,  is  a  general  anesthetic 
prepared  by  distilHng  a  mixture  of  chlorinated  lime  and  acetone. 
Alcohol  and  water  were  formerly  used  in  place  of  acetone  (see 
Exp.  70,  page  383).  While  it  is  not  regarded  as  inflammable, 
its  heated  vapor  can  be  made  to  burn  with  a  greenish  flame. 
The  reaction  with  alcohol  is  probably  as  follows:  4  C2II5OII 
+  8  Ca(C10)2  =  2  CHCI3  +  3  Ca  (CH02)2  +  5  CaCl2  +  8  H2O. 

Methyl  Chloroform,  CH3CCI3,  formed  by  replacing  the  hydro- 
gen atom  of  chloroform  by  a  methyl  group,  CH3,  has  been  used 
as  an  anesthetic. 

Tetrachloride  of  carbon  is  a  colorless  liquid  used  quite  largely 
as  a  solvent.  It  also  has  anesthetic  properties  but  like  dichlor- 
methane,  is  dangerous  because  of  its  action  on  the  heart. 

Methyl  bromide,  or  monobrom-methane,  is  used  to  some  ex- 
tent as  a  constituent  of  anesthetics. 

Bromoform-,  CHBr3,  tribrom-methane,  is  prepared  from 
bromine  and  a  solution  of  alcoholic  potash.  Its  properties  are 
similar  to  those  of  chloroform,  but  it  is  more  poisonous. 

Methyl  Iodide,  CH3I,  is  a  heavy  Hquid,  with  pleasant  odor, 
boiling-point  43°  C;  has  been  used  somewhat  as  a  vesicant. 


204  ORGANIC  CHEMISTRY 

Iodoform,  CHI3,  tri-iodomethane,  is  a  much-used  and  very 
valuable  antiseptic.  It  is  a  light-yellow  crystalline  powder 
with  characteristic  persistent  odor  (Plate  V,  Fig.  i,  page  204). 

Iodoform  may  be  made  by  heating  in  a  retort  two  parts  of 
potassium  carbonate,  two  of  iodine,  one  of  strong  alcohol,  and 
five  of  water,  till  the  mixture  is  colorless, 

C2H5OH  +  4 12  +  3  K2CO3  =  CHI3  +  KCHO2  +  5  KI  +  2  H2O 

+  3  CO2. 

Iodoform  is  also  produced  from  action  of  the  above  reagents 
with  acetone  in  place  of  alcohol.  This  test  is  a  very  delicate 
one  and  advantage  is  taken  of  it  in  testing  for  acetone  in  saliva, 
which  see. 

Cacodyl  is  an  example  of  the  arsenic  derivatives  of  the 
hydrocarbons.  It  is  one  of  several  products  which  result  from 
the  distillation  of  a  mixture  of  potassium  acetate  and  white 
arsenic.     Its  composition  is  that  of  dimethylarsine,  (CH3)2As. 

Ethyl  Chloride,  C2H5CI,  chlorethyl,  may  be  made  by  dis- 
tillation of  a  mixture  of  alcohol  and  hydrochloric  acid  and 
purification  of  the  distillate.  It  is  extremely  inflammable,  boils 
at  12°  C,  and  is  used  as  a  local  anesthetic  in  similar  manner  to 
methyl  chloride.  Its  higher  boiling-point  makes  it  the  more 
convenient  of  the  two  preparations  (see  page  178). 

Ethyl  Bromide,  C2H5Br,  prepared  from  alcohol,  sulphuric 
acid,  and  potassium  bromide.  It  is  a  heavy  colorless  liquid, 
does  not  burn,  and  has  been  used  to  considerable  extent  as  a 
general  anesthetic. 


PLATE  v.— ORGANIC  CHEMISTRY. 


Fig.  I. 
Iodoform. 


Fig.  3. 
Urea  Nitrate. 


Fig.  4. 
Hippuric  Acid. 


Fig.  5. 
Benzoic  Acid  (sublimed). 


Fig.  6. 
Tvrosin. 


CHAPTER  XXII. 
ALCOHOLS. 

If  we  substitute  for  one  of  the  hydrogen  atoms  of  methane, 
a  hydroxyl  group  (OH),  we  shall  produce  the  first  of  a  series  of 
alcohols,  several  of  which  will  claim  our  attention. 

The  alcohols  may  be  considered  as  hydroxides  of  alkyl  *  radi- 
cals, CH3OH  being  methyl  alcohol;  C2H5OH  being  ethyl  or 
ordinary  alcohol;  C3H7OH  being  propyl  alcohol;  and  C5H11OH, 
amyl  alcohol  or  fusel  oil. 

The  alcohols  as  a  class  may  be  prepared  by  the  action  of 
moist  silver  oxide  on  the  corresponding  halogen  compounds;  e.g., 

CHsBr  +  AgOH  =  CH3OH  +  AgBr. 

In  many  instances,  the  alkaline  hydroxides  will  act  in  the 
same  way. 

CHsBr  -I-  KOH  =  CH3OH  +  KBr. 

Alcohols  treated  with  metallic  sodium  or  potassium  liberate 
hydrogen  gas,  forming  compounds  known  as  alcoholates;    e.g., 

CH3OH  +  K  =  CH3OK  +  H; 
or  C2H5OH  +K  =  C2H5OK  +  H. 

While  these  compounds  are,  as  just  stated,  called  alcoholates, 
they  may  be  distinguished,  one  from  another,  by  using  the  name 
of  the  alkyl  radical  involved,  and  CH3OK  will  be  potassium 
methylate,  while  C2H5OK  will  be  potassium  ethylate. 

Alcohols  may  contain  tnore  than  one  hydroxyl  group,  and, 
according  to  number  of  the  OH  groups,  are  termed  mono-,  di-, 

*  Alkyl  —  a  term  used  to  denote  any  hydrocarbon  radical  as  CH3-,  CaHe-,  CsHr, 
etc. 

205 


2o6  ORGANIC  CHEMISTRY 

tri-atomic,  etc.  Thus,  ordinary  alcohol,  C0H5OH,  is  mono- 
atomic;  glycol,  C2H4(OH)2,  is  diatomic;  glycerol,  C3H5(OH)3, 
is  triatomic,  while  mannite,  C6H8(OH)g,  is  a  hexatomic  alcohol. 

Alcohols  may  also  be  classified  according  to  the  relative 
position  of  the  hydroxyl  group.  By  this  classification,  we  may 
have  primary  alcohols  with  OH  replacing  a  hydrogen  of  the 
—  CH3  group;  secondary  alcohols  with  OH  replacing  the  hydro- 
gen of  a  —  CHo  group;  and  tertiary  alcohol  with  OH  replacing 
the  hydrogen  of  a  —  CH  group.  This  may  be  illustrated  by 
the  formula  of  an  alcohol  of  each  class.  CH3  — CH2  — CH3, 
being  the  hydrocarbon,  a  primary  alcohol  will  have  the  formula 
CH3.CH2.CH2OH,  and  —  CHoOH  may  be  considered  distinctive 
grouping  of  the  primary  alcohols.  Again  from  the  same  hydro- 
carbon, if  OH  is  substituted  for  an  H  of  CHo  then  the  secondary 
alcohol  will  be  CH3-CHOH-CH3  and  -CHOH  may  be 
regarded  as  a  distinctive  group  of  this  class. 

The  tertiary  alcohols,  however,  must  be  produced  from  com- 
pounds having  at  least  four  carbon  atoms,  as  a  CH  group  is 
only  possible  when  there  are  sufficient  carbon  atoms  to  produce 
a  forked  chain;  that  is,  in  a  compound  with  three  carbon  atoms, 
one  must  of  necessity  be  placed  between  the  other  two,  while 
with  four  carbon  atoms,  the  carbons  may  be  attached  in  a 
straight  chain,  such  asC  —  C  —  C  —  C,  or  they  may  be  arranged  as 

/C 
a  forked  chain  C  —  C        ,  and  by  supplying  the  hydrogen  atoms 

necessary  to  satisfy  the  valence  of  each  carbon,  in  this  latter 
chain  we  find  a  CH  group.  OH  introduced  in  place  of  the 
hydrogen  of  this  group  gives  us  the  tertiary  alcohol, 

/CH3 
CH3-C0Hf 

Methyl  Alcohol,  CH3OH,  (H-CH2OH),*  wood  spirit,  car- 
binol,  is  a  product  of  the  destructive  distillation  of  wood  or  can 
*  Note  that  CH2OH  is  the  "alcohol  group"  peculiar  to  this  class  of  alcohols. 


ALCOHOLS  207 

be  made  synthetically  from  methane.  It  is  a  colorless,  inflam- 
mable liquid,  with  a  gravity  of  0.802  at  15°-  C,  with  solvent 
properties  similar  to  ordinary  alcohol.     It  boils  at  66°. 

Ethyl  Alcohol,  C2H5OH,  (CH3-CH2OH),  methyl  carbinol, 
grain  alcohol,  or  ordinary  alcohol  may  be  made  by  the  action  of 
silver  hydrate  on  ethyl  iodide  or  bromide  as  suggested  on  page 
205.  It  is  made  commercially  by  fermentation  of  various  car- 
bohydrates and  purified  by  distillation.  Carbon  dioxide  is 
evolved  as  follows: 

CeHioOe  =  2  C2H5OH  -f-  2  CO2. 

95%  alcohol  has  a  specific  gravity  0.8164,  boils  at  about 
78°  C,  dissolves  many  inorganic  salts,  vegetable  waxes,  resins 
(not  gums),  oils,  etc.,  and  is  miscible  with  water,  ether,  or  chlo- 
roform. 

Propyl  Alcohol,  normal,  CII3.CH2.CH2OH,  occurs  with  amyl 
alcohol  as  a  constituent  of  fusel  oil,  or  may  be  prepared  by 
general  method  with  moist  silver  oxide.  It  is  a  colorless  Hquid, 
boils  at  97°  C.  The  iso-compound,  CH3.CHOH.CH3,  may  be 
made  by  reducing  acetone  with  nascent  hydrogen;  nascent 
hydrogen  may  be  produced  by  sodium  amalgam. 

Butyl  Alcohol,  C4H9OH,  occurs  in  four  isomeric  forms.  The 
normal  alcohol  is  CH3.(CH2)2.CIl20H.  It  is  produced  by  the 
fermentation  of  glycerol.  It  boils  at  117°  C.  The  isobutyl  al- 
cohol, (0113)2. CII.CH2OH,  obtained  from  fusel  oil,  boils  at  107°  C. 

Amyl  Alcohol,  C5H11OH,  (C4H9  —  CH2OH),  consists  of  about 
87%  of  isobutyl  carbinol  and  about  13%  of  an  isomer  known 
as  active  amyl  alcohol.  It  is  a  colorless,  oily  hquid  with  a 
specific  gravity  of  0.818.  It  boils  at  about  130°  C,  and  burns 
with  a  bluish  flame. 

Fusel  oil,  or  potato  spirit,  consists  of  amyl  alcohol  carrying 
traces  of  various  other  alcohols  as  impurities. 

Amyl  alcohol  is  a  valuable  solvent  and  is  largely  used  in  the 
manufacture  of  artificial  fruit  flavors,  banana  essence,  and  the  Hke. 


208  organic  chemistry 

Oxidation  of  the  Alcohols. 
Aldehydes. 

The  first  step  in  the  oxidation  of  an  alcohol  consists  not  in 
the  addition  of  oxygen  but  in  the  withdrawal  of  hydrogen;  thus 
the  oxidation  of  methyl  alcohol  produces  formaldehyde  (CH2O) 
and  water. 

CH3OH  +  O  =  CH2O  +  HoO. 

Aldehydes  may  be  considered  compounds  containing  an  alkyl 

H  H 

/  I 

radical  and  a  distinctive  group,  —  C  ;  thus  CHO  is  formaldehyde, 

O 
CH3  is  acetaldehyde,  etc.     (Compare  Alcohol,  page  206.) 
I 
CHO 

Formaldehyde  coagulates  albumin  and  hardens  gelatin ;  when 
used  as  a  preservative  it  renders  the  proteins  tougher  and  less 
digestible. 

Formaldehyde  polymerizes,  producing  the  paraform  or  para- 
formaldehyde of  trade,  trioxymethylene,  with  a  probable  for- 
mula of  (CH20)3.  It  also  forms  one  lower  polymer  (CH20)2  and 
at  least  one  higher,  formose,  a  substance  allied  to  glucose. 

Acetaldehyde,  aldehyde,  CH3  — CHO  or  C2H4O,  the  aldehyde 
from  ethyl  alcohol,  may  be  made  by  addition  of  H2SO4  to  a 
mixture  of  alcohol  and  bichromate  of  potassium.  It  is  a  color- 
less, inflammable  liquid  with  pungent  etherial  odor  and  boils 
at  22°  C. 

Paraldehyde,  (C2H40)3,  a  polymer  of  acetaldehyde,  is  a  "color- 
less liquid  with  a  strong  pungent  odor,  soluble  in  8.5  parts  of 
water  at  15°  C,  miscible  in  all  proportions  with  alcohol,  ether, 
and  fixed  or  volatile  oils."     (U.  S.  P.)     It  is  a  valuable  hypnotic. 

Chloral,  CCI3CHO,  trichloraldehyde,  is  an  oily  Hquid  formed 
by  action  of  dry  chlorine  gas  on  pure  alcohol;  soluble  in  ether  and 


ALCOHOLS  209 

chloroform,  boiling  at  from  94°  C.  to  98°  C,  and  forming,  with 
a  molecule  of  water  chloral  hydrate,  CCI3CHO.H2O,  a  crystalline 
solid,  and  this  is  the  chloralum  hydratum  of  the  pharmacopoeia 
(seepage  176). 

Cliloral  hydrate  is  decomposed  by  sodimn  or  potassium 
hydrate  with  Hbcration  of  chloroform  (see  Exp.  87,  page  387): 
CCI3-CHO  +  KOH  =  CHCI3  +  KCOOH  (potassium  formate). 
Upon  warming  a  drop  or  two  of  aniline  oil  in  an  excess  of 
alcohoHc  potash,  chloral  hydrate  forms,  first,  chloroform,  then 
phenylisocyanide,  CeHsNC,  the  persistent  disagreeable  odor  of 
which  furnishes  a  delicate  test  for  chloroform  or  chloral  (see 
Exp.  88,  page  387).  By  using  CHCI3  as  the  reagent  in  place  of 
the  aniline,  the  same  reaction  becomes  a  test  for  aniline  or 
organic  compounds,  from  which  aniline  may  be  produced  by 
heating  with  alcoholic  potash  as  acetanihde.  Other  aldehydes 
from  hexatomic  alcohols  are  dextrose  (glucose)  and  galactose. 
They  are  represented  by  the  formula  CHoOH-  (CH0H)4-CH0, 
and  will  be  considered  more  fully  in  a  subsequent  lecture. 

'  Ketones. 

The  oxidation  of  secondary  alcohols  (page  206)  will  not  yield 
aldehydes,  but  a  class  of  substances  known  as  ketones : 

(CH3)2-CH-CHOH-CH3  +  O  =  (CH3)2-CH-C  :  O-CH3  +  H2O, 

A  secondary  alcohol.  Methyl  isopropyl  ketone. 

Methyl  isopropyl  carbinol. 

or        CHs  -  CHOH  -  CH3  +  O  =  CH3  -  CO  -  CH3  +  H2O. 

Isopropyl  alcohol.  Dimethyl  ketone. 

The  converse  of  each  of  these  reactions  is  possible,  and,  by 
reduction  of  a  ketone  with  nascent  hydrogen  (sodium  amalgam), 
the  secondary  alcohol  will  be  formed: 

CH3-CO-CH3  +  H  =  CH3-CHOH-CH3. 

Acetone.  Isopropyl  alcohol. 


2IO  ORGANIC  CHEMISTRY 

Likewise  primary  alcohols  may  be  produced  by  the  reduc- 
tion of  aldehydes : 

CH3  -  CHO  +  H>  =  CH3  -  CHoOH. 

Acetaldeliyde.  Ethyl  alcohol. 

Note  that  the  grouping  peculiar  to  ketones  is  =  CO  or  —  CO  — . 

Acetone,  or  dimethylketone,  CH3  — CO  — CH3,  a  colorless 
liquid  of  peculiar  odor,  boils  at  56°  C.  and  is  made  commercially 
by  the  dry  distillation  of  acetate  of  lime. 

It  occurs  in  the  blood  and  urine  of  patients  suffering  from 
advanced  diabetes.  According  to  von  Noorden,  the  acetone 
found  in  the  blood  is  formed  by  an  intracellular  process  and  in- 
dicates an  acid  auto-intoxication  and  an  insuflficient  utilization 
of  carbohydrates.  In  the  experience  of  the  author,  acetone 
may  sometimes  be  found  in  the  saliva  when  it  cannot  be  found 
in  the  urine  (for  test,  see  Acetone  under  SaHva  and  Urine). 

Another  ketone  of  interest  is  levulose,  fruit-sugar,  CH2OH  — 
CHOH.CHOH.CHOH.CO.CH2OH,  which,  with  glucose,  will  be 
studied  later. 

While  the  oxidation  of  a  primary  alcohol  will  produce  an 
aldehyde  and  the  oxidation  of  a  secondary  alcohol  will  produce 
a  ketone,  the  tertiary  alcohol,  by  action  of  an  oxidizing  agent, 
is  split  into  two  new  carbon  compounds,  that  is,  the  chain  is 
broken  and  simpler  compounds  usually  including  an  organic  acid 
are  formed. 


CHAPTER  XXIII. 
ETHERS. 

Ethers  may  be  regarded  as  oxides  of  the  hydrocarbon  radi- 
C2H5 
cals,  as  ^O,  or  as  anhydrides  of  the  monatomic  alcohols, 

C2H5 

water  having  been  removed  from  two  molecules  of  the  alcohol: 

2  C2H5OH  -  H2O   =    (C2H5)20. 

Ethers  may  be  simple,  mixed,  or  compound.  The  simple 
ether  is  illustrated  above  by  the  formula  for  ordinary  or  ethyl 
ether,  where  two  radicals  of  the  same  kind  are  united  by  an 
atom  of  oxygen. 

In  a  mixed  ether,  these  radicals  will  be  of  different  kinds; 
as,  for  example,  CH3  — 0  — C2H5,  methyl-ethyl  ether. 

The  compound  ethers  are  compounds  of  alcohol  radicals 
with  acid  radicals,  that  is,  the  salts  of  alcohol  radicals.  The 
acid  may  be  either  organic  or  inorganic;  thus,  we  have  nitric 
ether,  ethyl  nitrate,  C2H5NO3,  and  we  have  acetic  ether,  ethyl 
acetate,  C2H5C2H3O2.  The  compound  ethers  are  often  called 
esters  and  form  a  large  and  important  class  of  organic  com- 
pounds. 

A  general  method  for  the  preparation  of  simple  and  mixed 
ethers  is  that  of  distillation  of  the  corresponding  alcohols  with 
sulphuric  acid,  as  illustrated  by  experiment  No.  94,  page  388. 
They  may  also  be  produced  by  the  action  of  silver  oxide  on  the 
corresponding  alkyi  iodides: 

-    2  C2H5I  +  Ag20  =  (C2H5)20  +  2  Agl, 
also,  by  treating  the  sodium  alcoholate  with  an  alkyl  iodide^ 


212  ORGANIC  CHEMISTRY 

CsHsONa  +  C2H5I  =  (CoH5)20  +  Nal 

CH3\ 
or  CHsONa  +  C0H5I  =  O  +  Nal. 

Methyl  Ether.  —  Methyl  oxide,  (CH3)20,  also  known  as 
formic  ether,  is  isomeric  with  ordinary  alcohol,  and  may  be  made 
in  a  manner  similar  to  that  used  in  the  production  of  ethyl  ether 
{q.v.).  At  ordinary  temperature  it  is  a  gas,  but  liquefies  at 
—  20°  C.  (Bernthsen).  It  has  been  used  as  a  general  anesthetic, 
and  the  anesthesia  is  said  to  be  profound  and  quickly  pro- 
duced (U.  S.  D.  from  A.  J.  P.,  Sept.,  1870). 

Methyl-ethyl  Ether.  —  This  name,  besides  indicating  a 
definite  compound  as  referred  to  in  the  preceding  paragraph, 
has  been  applied  to  a  mixture  of  methyl  ether  and  ethyl  ether, 
used  for  purposes  of  general  anesthesia. 

Methylene  Ether.  —  A  name  applied  to  a  mixture  of  methyl- 
ene dichloride  and  ethyl  ether,  used  as  an  anesthetic,  but  it  has 
been  found  unsafe  (U.  S.  D.). 

Ethyl  Ether.  —  Ethyl  oxide,  (C2H5)20.  The  ether  used  for 
general  anesthesia  should  contain  not  less  than  95^%  or  more 
than  97^%  of  ethyl  oxide,  the  remainder  consisting  of  alcohol 
with  a  little  water  (U.  S.  P.)-  It  is  a  light  colorless  Uquid 
with  a  specific  gravity  of  0.715  at  25°  C,  with  a  boiling-point  of 
about  35°  C.  It  may  be  made  by  the  action  of  sulphuric  acid  on 
ethyl  alcohol,  and  from  this  fact  has  been  known  as  sulphuric 
ether,  but  this  name  is,  of  course,  incorrectly  used,  sulphuric 
ether  being  properly  an  ethyl  sulphate,  (C2H5)oS04. 

In  the  preparation  of  ether,  sulphuric  acid  may  be  mixed  with 
rather  more  than  its  own  bulk  of  alcohol,  the  mixture  heated  to 
a  temperature  of  from  130°  to  138°  C.  in  a  suitable  retort  or 
still,  the  distillate  (ether)  being  collected  in  a  cold  receiver. 

The  reaction  takes  place  in  two  steps,  as  follows:  One  mole- 
cule of  acid  and  one  of  alcohol  react  to  form  ethyl  sulphuric 


ETHERS 


213 


acid  (ethyl  acid  sulphate)  and  H2O,  H2SO4  +  C.HsOH  = 
C2H6HSO4  +  H2O.  Then  the  ethyl  sulphuric  acid  reacts  with 
a  second  molecule  of  alcohol  to  form  ether  and  sulphuric  acid, 
C2H8HSO4  +  C2H5OH  =  (CoH5)2C  +  H2SO4.  Thus  the  sul- 
phuric acid,  from  two  molecules  of  alcohol,  has  produced  one 
molecule  of  ether  and  is  in  condition  to  repeat  the  process,  hav- 
ing been  changed  only  to  the  extent  of  adulteration  with  one 
molecule  of  water.  In  accordance  with  this  theoretic  forma- 
tion of  ether  by  simple  dehydration  of  alcohol  by  sulphuric  acid, 
provision  is  made  for  a  continuous  process,  by  the  introduction  of 
a  constant  supply  of  fresh  alcohol  into  the  retort  during  the  dis- 
tillation, and  so  regulated  that  the  total  bulk  of  liquid  is  neither 
increased  nor  diminished.  The  product  is  then  purified,  and 
freed  from  water  and  traces  of  acid  by  redistillation  over  a  mix- 
ture of  lime  and  calcium  chloride. 

Ether,  according  to  the  U.  S.  P.  requirements,  is  "  a  trans- 
parent, colorless,  mobile  liquid  with  characteristic  odor  and  a 
burning  and  sweetish  taste." 

It  is  soluble  in  about  twelve  times  its  volume  of  water  and 
in  all  proportions  in  alcohol,  chloroform,  petroleum  ether,  ben- 
zene, and  oils.  It  is  readily  inflammable,  and  this  fact,  together 
with  its  easy  volatility,  makes  it  necessary  to  use  considerable 
care  when  handling  it. 

The  action  of  sulphuric  acid  upon  alcohol  needs  careful 
regulation;  because  there  may  be  produced  three  other  products 
in  addition  to  the  ethyl  oxide  already  considered.  These  are, 
first,  ethyl  sulphuric  acid,  C2H5HSO4;  second,  ethyl  sulphate 
(02115)2804,  these  being  respectively  the  acid  and  neutral  ethyl 
esters  of  H2SO4;  third,  the  hydrocarbon  ethylene,  C2H4.  This 
latter  compound  is  the  first  of  the  ethylene  series  of  hydro- 
carbons with  the  general  formula  C„Il2„  and  containing  ^'  double- 

H\  /H 

bonded  "  carbon  atoms,        C  =  C  or    CH.  =  CH.CH3. 


214  ORGANIC  CHEMISTRY 

These  are  unsaturated  hydrocarbons  (see  page  201).  Ethylene 
is  produced  by  the  action  of  an  excess  of  concentrated  sulphuric 
acid,  which  abstracts  water  from  each  molecule  of  alcohol 
(C2H5OH  —  H2O  =  C2H4),  whereas  in  the  preparation  of  ether 
the  more  dilute  acid  abstracts  water  from  two  C2H5OH. 

Compound  Ethers  or  Esters. 

Ester  is  the  term  applied  to  etherial  salts;  that  is,  compounds 
in  which  an  alkyl  group  has  taken  the  place  of  replaceable  hy- 
drogen of  the  acid.  They  are  produced  by  the  action  of  the  acid 
upon  the  alcohol  which  is  as  nearly  as  possible  free  from  water. 

Such  action  by  the  halogen  acids  would  produce  the  alkyl 
haloids  already  considered;  for  example,  CH3OH  +  HCl  = 
CH3CI  +  HoO.  As  the  water  produces  alcohol  and  hydro- 
chloric acid  by  action  on  CH3CI  it  must  be  removed  as  the 
experiment  proceeds. 

The  ethyl  hydrogen  sulphate  is  produced  as  an  intermediate 
step  in  the  preparation  of  ether,  q.v. 

Ethyl  nitrite,  C2H5NO2,  is  a  colorless  liquid,  boiling  at  17°  C. 
and  is  used  in  medicine  as  Sweet  Spirits  of  Niter,  which  is  an 
alcoholic  solution  containing  traces  of  the  ethyl  nitrate,  various 
oxidation  products,  and  not  less  than  3.5%  nor  more  than  4.5% 
of  the  ethyl  nitrite.  It  is  insoluble  in  water,  but  by  action  of 
boiling  water  or  dilute  alkalies  becomes  ethyl  alcohol,  C2H5NO2  + 
KOH  =  C0H5OH  +  KNO2.     See  Exp.  97. 

Ethyl  Acetate,  CH3  — COO.C2H5,  is  formed  by  heating  ethyl 
alcohol,  sulphuric  acid,  and  acetate  of  sodium.  This  reaction 
constitutes  a  qualitative  test  for  acetic  acid  or  acetates,  the 
odor  of  the  ester  being  sufficiently  characteristic  to  furnish  a 
delicate  test  (page  100). 

The  acetic  ether  of  the  U.  S.  P.  is  "a  liquid  composed  of 
about  98.5%  of  ethyl  acetate  and  1.5%  alcohol." 

Ethyl  Butyrate,  CH3  -  CHo  -  CH2  -  COOC2H5.  This  ester 
dissolved  in  ten  parts  of  alcohol  forms  pineapple  essence.     It 


ETHERS  215 

may  be  made  in  a  manner  similar  to  the  preparation  of  ethyl 
acetate,  i.e.,  by  heating  together  alcohol,  butyric  acid,  and 
concentrated  sulphuric  acid.  The  production  of  the  ester  is 
likewise  used  as  a  qualitative  text  for  the  presence  of  the  acid, 
and  employed  in  the  examination  of  gastric  contents  as  follows: 
"  Heat  10  c.c.  of  contents  with  5  c.c.  of  strong  sulphuric  acid 
and  4  c.c.  of  95%  alcohol;  odor  of  pineapple  indicates  butyric 
acid."     (Hewes.) 

Amyl  Acetate  and  Amyl  Butyrate  may  be  obtained  by  heat- 
ing the  respective  acids  with  amyl  alcohol  (CsHnOH)  and  strong 
sulphuric  acid.  These  esters  may  also  be  used  in  detecting  the 
presence  of  the  acid,  amyl  alcohol  being  used  in  place  of  ordinary 
alcohol.  Amyl  acetate  gives  the  odor  of  pears,  amyl  butyrate 
that  of  bananas. 

Amyl  nitrite,  C5H11NO2,  is  a  compound  used  in  medicine  to  a 
considerable  extent,  usually  administered  by  inhalation.  The 
U.  S.  P.  preparation  contains  about  80%  of  amyl  nitrite.  It  is 
very  soluble  and  inflammable. 

Fats  are  esters  of  glyceryl,  C3H5,  also  called  tritenyl, 
propenyl,  etc.  This  radical  forms  with  hydroxyl  (OH)  the  pro- 
penyl  alcohol,  C3H5(OH)3,  which  is  ordinary  glycerin  or  glycerol. 

Glyceryl  butyrate  or  butyrin,  CH3-(CH2)2-COOC3H5,  con- 
stitutes (together  with  smaller  quantities  of  the  glyceryl  esters 
of  capric,  caproic,  and  caprylic  acids)  about  7%  of  butterfat. 
These  esters  are  readily  saponified  by  treatment  with  alcoholic 
potash;  then,  by  decomposition  of  the  potassium  salts  with 
H2SO4,  the  acids,  being  volatile,  may  be  separated  by  distillation. 
The  amount  of  volatile  fat  acids  thus  obtamed  is  a  valuable  test 
for  the  genuineness  of  the  butter. 

For  further  consideration  of  fats  see  Chapter  XXXI. 


CHAPTER  XXIV. 
ORGANIC  ACIDS. 

If  the  oxidation  of  an  alcohol  is  carried  beyond  the  formation 
of  aldehyde  or  ketone,  i.e.,  if  the  aldehyde  or  ketone  be  oxidized, 
an  organic  acid  results.  The  first  atom  of  oxygen  involved  in 
this  process  does  not  become  a  constituent  part  of  the  new 
molecule,  but  simply  withdraws  hydrogen  from  the  old  (the 
alcohol),  as  shown  in  the  formation  of  aldehydes  on  page  208. 
The  second  atom  of  oxygen,  however,  attaches  itself  to  the 
molecule  and  does  become  a  part  of  the  new  substance  (the  acid) : 

CH3  CH3  CII3  CH3 

I      +0=1      +  H2O    I      +0=1 

CHoOH  CHO  CHO  COOH 

Alcohol.  Aldehyde.  Aldehyde.  Acid. 

The  group  —COOH  is  known  as  carboxyl  and  is  the  char- 
acteristic group  of  the  acids.  The  hydrogen  of  the  carboxyl 
differs  from  the  other  atoms  of  hydrogen  in  the  molecule  in  that 
it  is  united  to  oxygen  rather  than  to  carbon,  and  constitutes  the 
basic  or  replaceable  hydrogen  of  the  acid;  hence  acetic  acid  is 
monobasic,  and  the  only  possible  salt  of  potassium,  for  instance, 
isCHa-COOK. 

The  basicity  of  the  acid  depends  on  the  number  of  carboxyl 
groups  it  contains. 

Among  the  monobasic  acids  of  the  fatty  or  paraffin  series 
which  we  will  study  are  the  follomng: 

Representative  Fatty  Acids. 

H.COOH  =  formic  acid  or  hydrogen  formate; 

CH3.COOH  =  acetic  acid  or  hydrogen  acetate; 

216 


ORGANIC   ACIDS  217 

C2H5.COOH  =  propionic  acid  or  hydrogen  propionate; 

C3H7COOH  =  butyric  acid  or  hydrogen  butyrate; 

C4H9COOH  =  valeric  acid  or  hydrogen  valerate; 
C15H31COOH  =  palmitic  acid  or  hydrogen  pahnitate; 
C17H35COOH  =  stearic  acid  or  hydrogen  stearate. 

The  acids  of  these  series  are  represented  by  the  general 
fonnula  C„H2„02.  They  all  are  monobasic;  i.e.,  they  contain 
only  one  atom  of  replaceable  hydrogen. 

Formic  Acid,  (H.COOH),  originally  distilled  from  the  bodies 
of  ants  (formica,  from  which  the  name  is  derived) ,  is  a  colorless, 
easily  volatile  liquid.  It  may  be  prepared  in  the  laboratory 
by  heating  oxaHc  acid  with  glycerol,  when  the  oxalic  acid  breaks 
up  into  formic  acid  and  CO2. 

C2H2O4  =  CO2  +  CHOOH. 

Carbon  monoxide,  passed  over  hot  potassium  hydroxide, 
results  in  the  formation  of  potassium  formate, 

CO  +  KOH  =  HCOOK. 

Also  by  treatment  of  ammonium  carbonate  with  nascent  hydro- 
gen (sodium  amalgam), 

C03(NH4)2  +  2  H  =  HC00(NH4)  +  H.O  +  NH3 
and 

HC00(NH4)  +  NaOH  =  HCOONa  +  NH3  +  H.O. 

Formic  acid,  according  to  the  above  reaction,  is  apparently 
carbonic  acid  less  one  atom  of  oxygen,  and  the  fact  that  formic 
acid  acts  easily  as  a  reducing  agent,  taking  away  oxygen  from 
other  bodies  and  becoming  H2CO3,  is  further  proof  of  this 
relationship. 

Acetic  Acid,  CH3COOH,  is  obtained  commercially  by  the 
oxidation  of  ethyl  alcohol.  It  is  the  acid  of  vinegar,  which, 
according  to  Massachusetts  law,  should  contain  4^%  of  acid. 
Glacial  acetic  acid  is  a  commercial  name  of  the  acid  contain- 
ing 1%  of  less  of  water;   it  is  a  colorless  soHd  at  a  temperature 


2l8  ORGANIC  CHEMISTRY 

below  15°  C.  The  U.  S.  P.  acetic  contains  only  36%  (by  weight) 
of  the  pure  acid. 

Either  one,  two,  or  all  three  of  the  hydrogen  atoms  of  the 
CH3  group  may  be  replaced  by  chlorine,  forming  respectively 
the  mono-,  di-,  and  tri-chloracetic  acids,  the  trichloracetic  acid 
being  used  to  a  considerable  extent  in  dentistry  (page  187). 

Acetic  acid,  by  the  abstraction  of  water,  forms  an  anhydride, 

2  HC2H3O2   =    (C2H30)20  +  H2O. 

This  substance  is  of  considerable  importance  in  organic  reac- 
tions. It  is  a  colorless  hquid  with  a  boiling-point  of  138°  C, 
and,  with  the  halogens,  forms  compounds  such  as  acetyl  choride, 
C2H3OCI,  the  radical  C2H3O  being  known  as  the  acetyl  radical. 

Propionic  acid,  CH3.CH2.COOH,  is  a  colorless  hquid,  boihng 
at  140°  C.  According  to  Witthaus,  it  is  best  prepared  by 
heating  ethyl  cyanide  with  caustic  potash  until  the  odor  of  the 
ester  has  disappeared: 

C2H5CN  -f-  KOH  +  H2O  =  C2H5COOK  -f  NH3. 

Then,  by  treatment  with  H2SO4,  the  propionic  acid  is  Uberated, 
and  may  be  separated  by  distillation. 

Butyric  Acid,  C3H7COOH,  occurs  as  a  product  of  fermenta- 
tion of  butter,  or  other  animal  fat  containing  butyrin;  also 
from  the  decomposition  of  lactic  acid,  two  molecules  of  lactic 
acid  furnishing  one  of  butyric  acid,  two  of  carbon  dioxide  and 
two  of  hydrogen  (Ho).  It  is  an  occasional  constituent  of  the 
gastric  contents,  and  may  be  detected  by  formation  of  the  ethyl 
ester  (page  215).  The  pure  acid  is  a  heavy,  colorless  hquid  with 
characteristic  odor,  soluble  in  water  in  any  proportion.  See 
page  215  for  the  glyceryl  ester  of  butyric  acid  (butyrin);  also 
for  stearic  and  palmitic  acids. 

Valeric  Acid,  C4H9COOH,  may  be  made  by  the  oxidation  of 
amyl  alcohol  (C5H11OH).  It  is  an  oily  hquid  boihng  at  174°  C. 
It  occurs  as  a  constituent  of  valerian,  and  in  consequence  has 


ORGANIC  ACIDS  219 

been  called  valeric  acid.  Its  salts  are  used  in  medicine  as  seda- 
tives. 

The  valeriate  of  amyl  has  an  odor  resembUng  that  of  apples, 
and  is  used  in  alcoholic  solutions  as  apple  essence. 

Palmitic  Acid,  C15H31COOH,  a  solid  "  fat  acid,  "  occurs  as  a 
glyceryl  ester  in  butter  (to  a  very  slight  extent),  in  olive  oil, 
palm  oil,  and  ba^yberry  wax.  Combined  with  certain  alcohols 
it  occurs  in  white  and  yellow  wax;  also  in  spermaceti. 

Palnutin,  C3H5(Ci6H3iO-2)3,  occurs  in  all  animal  fat  and  in 
large  quantities  in  human  fat. 

Stearic  Acid,  Ci7H35COOH[CH3  -  (CH2)i6  -  COOH],  as  glyceryl 
stearate  or  stearin,  occurs  in  vegetable  and  animal  fats,  particu- 
larly in  tallow.  Stearic  acid  is  only  sKghtly  soluble  in  alcohol 
or  in  ether.     Its  melting-point  is  69.3°  C. 

Acrylic  Acid  Series. 

Acrylic  acid,  CHo  :  CH.COOH,  is  a  type  of  the  double- 
bonded  acids.  It  is  a  liquid  with  boiling-point  at  140°  C.  Nas- 
cent hydrogen  breaks  the  double  bond,  forming  propionic  acid, 
CH3.CH2.COOH.  Hydriodic  acid  will  also  break  the  double 
bond  by  direct  union  of  its  constituents,  forming  CH2I  — CH2 
—  COOH,  (/S-iodo  propionic  acid). 

Acrylic  aldehyde,  or  acrolein,  is  a  colorless  liquid  boiling  at 
52°  C.  Its  vapor  has  an  irritatmg,  pungent  odor,  sufficiently 
characteristic  to  be  used  as  a  quahtative  test  for  glycerol,  from 
which  it  is  obtained  by  heating  -uith  KHSO4. 

The  only  other  acid  of  particular  interest  in  this  series  is 
oleic  acid,  C17H33COOH.  It  is  an  important  constituent  of  oils, 
both  animal  and  vegetable. 

Its  glycer>d  ester,  C3H5(Ci7H33C02)3,  forms  a  large  part  of 
lard  oil,  cotton-seed  oil,  or  any  oil  obtained  by  cold  expression. 


220 


ORGANIC  CHEMISTRY 


Dibasic  Acids. 
COOH        COOH 


COOH 

Oxalic  acid. 


CH2 

I 

COOH 

Malonic  acid. 


COOH 

I 
CH2 

I 
CH2 

I 
COOH 

Succinic  acid. 


Dibasic  acids  contain  two  carboxyl  groups.     These  are  refer- 
able to,  and  in  many  cases  may  be  formed  from,  the  diatomic 

CH.OH 
alcohols.     Thus  glycol,     I  ,  upon  oxidation  yields  glycollic 

CH2OH 
CH2OH  COOH 

acid,    I  ,  and  oxalic  acid,    I 

COOH  COOH 

.OH 
Carbonic  acid,  O 


/ 


C  ^         ,  is  dibasic  in  that  it  contains  two 
^OH 

atoms  of  replaceable  hydrogen,  though  not  two  carboxyl  groups. 

It  is  claimed  that  a  molecule  of  this  sort  cannot  exist  because 

a  single  carbon  atom  cannot  hold  more  than  one  hydroxyl  group 

in  combination.     This  acid  has  never  been  isolated,  aU  attempts 

to  separate  it  in  the  pure  form  resulting  in  the  formation  of 

carbonic  acid  gas  and  water.     Its  compounds  (carbonates)  are 

very  common  and  very  important,  both  in  organic  and  inorganic 

chemistry.     Organic  salts  of  carbonic  acid  may  be  made  by 

treating  silver  carbonate  with  alkyl  iodide. 

/OAg  /OC2H5 

CO  +  2  C2H5I  =  CO  +2  Agl. 

■^OAg  ^OCaHs 

Oxalic  Acid,  which  may  be  considered  as  a  type  of  the  di- 
basic acids,  occurs  as  small,  colorless  crystals  (four-  or  six-sided 
prisms),  containing  two  molecules  of   water  of   crystallization 


ORGANIC  ACIDS  221 

(H2C2O4.2  H2O);  it  is  but  slightly  efflorescent,  and,  if  carefully 
crystallized,  is  suitable  for  the  preparation  of  standard  acid 
solution.  Salts  of  oxalic  acid  occur  in  many  plants;  the  acid 
potassium  oxalate,  "  salt  of  sorrel,"  is  found  in  common  red 
sorrel  (Rumex  acetora)  and  in  wood  sorrel  (Oxalis  acetocella). 
OxaKc  acid  in  various  combinations,  often  with  lime,  is  widely 
distributed  in  articles  of  vegetable  diet,  particularly  tomatoes, 
rhubarb,  spinach,  and  asparagus;  grapes,  apples,  and  cabbages 
also  carry  oxalates  but  in  smaller  amounts. 

The  source  of  oxalates  in  the  system  is  twofold,  —  the  in- 
gested oxalates  and  those  produced  by  oxidation,  incident  to 
metabolism,  the  exact  nature  of  which  has  not  been  clearly 
demonstrated  (see  Calcium  and  Sodium  Oxalates,  under  Urine 
and  SaHva) . 

Oxalic  acid  was  previously  made  commercially  by  the  action 
of  strong  nitric  acid  on  starch  or  sugar;  it  is  now  prepared  by 
heating  cellulose  (in  form  of  sawdust)  with  a  mixture  of  po- 
tassium hydroxide  and  sodium  hydroxide,  precipitating  the  acid 
as  CaC204,  and  decomposing  the  salt  by  sulphuric  acid.  The 
acid  is  then  purified  by  repeated  crystallization. 

Malonic  Acid,  COOH  — CH2  — COOH,  is  an  oxidation  product 
of  malic  acid  (from  apples),  and  is  comparatively  unimportant. 

Succinic  Acid,  COOH(CH2)2  — COOH,  occurs  in  amber,  from 
which  it  takes  its  name  (Amber-Succinum) .  It  has  been  de- 
tected in  the  urine  after  asparagus  and  some  fruits  have  been 
eaten.  It  occurs  as  colorless  crystals,  soluble  in  water,  and  only 
slightly  soluble  in  ether.  Succinic  acid  may  be  obtained  by  the 
saponification  of  ethylene  cyanide,  C2H4(CN)2,  and  is  a  dibasic 
acid  containing  four  carbon  atoms.  It  is  a  constituent  of  some 
transudates  and  cyst  fluids.  It  occurs  in  the  spleen  and  thyroid 
gland,  and  has  been  found  in  sweat  and  in  the  urine  (Ham- 
marsten) . 

Pyro-tartaric  Acid,  formed  by  the  distillation  of  ordinary  tar- 
taric acid,  is  one  of  four  isomers  of  formula  C5H8O4,  and  is  of 


222  ORGANIC  CHEMISTRY 

interest  only  in  its  relation  to  some  of  the  amino  acids  which 
result  from  protein  digestion.  Formula  for  pyro-tartaric  acid 
is  CH3  -  CHCOOH  -  CH2  -  COOH. 

Oxyacids. 

Hydroxy-acids,  or  alcohol  acids,  contain  hydroxyl  in  place 
of  one  or  more  hydrogen  atoms  of  the  fatty  acids.  Thus  we 
may  consider 

Carbonic  acid  as  hydroxyformic  acid,  HO  — COOH; 

CH.OH 
Glycollic  acid  as  hydroxy  ace  tic  acid,    I  ; 

COOH 

C2H4OH 
Lactic  acid  as  hydroxypropionic  acid,    I  ; 

COOH 

CHOH-COOH 

MaHc  acid  (from  apples)  as  hydroxy-  I 

succinic  acid,  CH2  —  COOH 

CHOH-COOH 
Tartaric  acid  as  dihydroxysuccinic  acid,  I 

CHOH-COOH 

Citric  Acid,  from  lemons,  limes,  etc.,  is  in  a  class  by  itself. 
It  is  a  tribasic  acid  (has  three  carboxyl  groups  and  one  hydroxyl) ; 
the  formula  is  C3H40H-(COOH)3. 

Glycollic  Acid  occurs  in  nature  in  unripe  grapes,  and  possibly 
as  antecedent  to  oxalates  in  the  system  (Dakin,  Journal  of  Biol. 
Chem.,  3.57).  Glycollic  acid  is  formed  from  glycol  by  oxidation, 
and  from  glycocoll,  by  action  of  nitrous  acid. 

Nitric  acid  will  oxidize  glycollic  acid  to  oxalic  acid. 

Lactic  Acid.  —  Oxypropionic  acid,  or  i  *-ethyHdene  lactic 
acid,  CH3  — CHOH-COOH,  is  ordinary  lactic  acid  produced  by 
fermentation  of  milk-sugar,  etc.     It  occurs  in  the  gastric  juice 

*  Optically  inactive. 


ORGANIC  ACIDS  223 

and  in  contents  of  the  intestine,  "  particularly  during  a  diet 
rich  in  carbohydrates,"  possibly  in  muscle  and  brain  tissue 
(Foster).     It  is  not  volatilized  at  temperatures  below  160°  C. 

Sarcolactic  or  paralactic  acid,  <;?*-ethylidene  lactic  acid, 
occurs  in  meat  extract.  The  presence  of  this  acid  causes  the 
acid  reaction  of  dead  muscle,  possibly  of  contracted  muscle. 
It  occurs  in  the  blood  and  at  times  in  the  urine,  and  it  is  probable 
that  it  is  this  modification  that  may  be  found  as  lactates  and 
acid  lactates  in  the  saliva  and  urine,  the  crystalHne  forms  of 
which  have  been  identified  by  Dr.  E.  C.  Kirk  of  Philadelphia, 
by  the  use  of  the  micropolariscopic  method  of  Dr.  Joseph  P. 
Michaels  of  Paris. 

The  optical  activity  of  the  lactic  acids  depends  upon  the 
presence  of  an  asymmetric  carbon  atom.  This  asymmetric 
carbon,  as  the  name  implies,  is  one  holding  four  different  groups 
or  atoms  as  illustrated  by  the  following  compounds. 

CH3\     /OH        (CoHsOs)^     /OH  H\      /CH2.COOH 

c  c  c 

H^     "^COOH  H^     ^COOH    HO^     _\COOH 

Lactic  Acid.  Tartaric  Acid.  MaJic  Acid. 

The  truth  of  the  above  statement  regarding  the  optical 
activity  of  these  substances  may  be  demonstrated  quite  readily 
by  the  reduction  of  the  hydroxyl  group  in  sarcolactic  acid  when 
the  inactive  propionic  acid  results. 

CH3\     /OH  CH3\     /H 

c  c 

H^     "^COOH  H^    ^COOH 

Active.  Inactive. 

The  optical  activity  consists  in  the  power  of  the  substance 
to  turn  the  ray  of  polarized  light  to  the  right  or  to  the  left. 

Both  of  these  acids  form  characteristic  crystalHne  salts  of 
zinc  and  of  calcium.     In  cold  water  the  zinc  sarcolactate  is 

*  Dextrorotary. 


224  ORGAXIC  CHEMISTRY 

more  soluble  than  zinc  lactate;   on  the  other  hand,  the  calcium 
sarcolactatc  is  rather  less  soluble  than  calcium  lactate. 

P-Oxybutyric  Acid,  CH3  -  CHOH  -  CH2  -  COOH.  If  there  is 
introduced  into  butyric  acid,  CH3-CH2-CH2-COOH,  an  OH 
group,  an  oxybutyric  acid  results.  If  this  alcohol  group  (OH) 
occupies  the  secondary  or  ^  position  (i.e.,  attached  to  the  carbon 
atom  twice  removed  from  the  carboxyl),  the  acid  is  the  /3-oxy- 
butyric  as  above. 

By  oxidation  of  the  compound,  the  alcohol  group  is  broken 
up  and  hydrogen  withdrawn  to  form  water,  lea\ing  a  keto  acid, 
CH3  — CO  — CH2  — COOH,  known  as  diacetic  acid.  This  in  turn 
may  give  off  carbon  dioxide  and  become  dimethyl  ketone,  or 
acetone,  CH3  —  CO  —  CH3.  These  three  substances,  ^S-oxybutyric 
acid,  diacetic  acid,  and  acetone,  are  classed  in  von  Noorden's 
"  Autointoxication,"  and  in  the  works  of  other  recent  writers, 
as  "  the  acetone  bodies,"  and  by  this  convenient  term  we  may 
refer  to  them  collectively.  They  occur  in  diabetic  urine  and, 
according  to  von  Noorden,  in  other  cases  of  perverted  oxidation 
(not  insuflEicient  oxidation). 

Tartaric  Acid  is  a  dihydroxysuccinic  acid,  COOH— (CH0H)2 
—  COOH,  obtained  from  grape-juice. 

We  see  by  an  examination  of  the  graphic  formula  of  this 
acid  that  it  contains  two  as}Tnmetric  carbon  atoms. 

rnnj^  By  placing  the  h}'drogen  or  the  hydroxyl 

I  on  similar  or  opposite  sides  of  the  chain  we 

jj  — C  — OH        see  how  it  might  be  possible  to  obtain  a 

I  new  form  of  isomerism  depending  on  the 

OH  — C  — H  relative  position  of  the  atoms  in  space  and 

'  not  at  all  upon  their  attachment  to  other 

atoms  of  the  molecule.     This  is  found  to 

be  the  fact  and  this  sort  of  isomerism  resulting  only  in  differing 

physical  properties   such  as  optical   activity  has   been   called 

physical  isomerism  or  stereo-isomerism. 

A  mixture  of  equal  weights  of  these  two  kinds  of  tartaric 


ORGANIC  ACIDS  225 

acid  crystallized  together  give  an  example  of  what  is  known  as 
di-  forms  or  racemic  compounds. 

The  double  tartrate  of  sodium  and  potassium  (Rochelle  salt), 
KNaC4H406,  is  much  used  in  medicine. 

Tartaric  acid  combines  with  potassium  and  antimony  to 
form  tartar  emetic,  (KSbOC4H406)2,  H2O. 

The  "  scale  salts  of  iron,^''  "  ferri  et  ammonii  tartras  "  and 
"  ferri  et  potassii  tartras,"  are  prepared  by  dissolving  freshly 
precipitated  ferric  hydroxide,  in  the  acid  tartrate  of  ammonia  or 
potash,  and,  after  evaporation  to  thick  syrup,  soHdifying  in 
thin  layers  on  glass  plates. 

Potassium  Bitartrate,  or  acid  tartrate,  KHC4H4O6,  is  cream 
of  tartar,  and  one  of  the  few  salts  of  potassium  only  sparingly 
soluble  in  water.     Its  commercial  source  is  the  wine-vat. 


Monobasic  Amino  Acids. 

Amino  acids,  formerly  called  amido  acids,  are  characterized 
by  an  NH2  group  in  place  of  hydrogen;  for  example,  acetic  acid  is 

CH3  CH2NH2 

I  .     Amino  acetic  acid  is    I  .     These  acids  are  of 

COOH  COOH 

particular  interest  because  of  their  close  relationship  to  protein, 
many  of  them  being  among  the  cleavage  products  of  protein 
hydrolysis. 

That  many  of  the  amino  acids  are  formed  as  intermediate 
steps  in  the  reduction  of  the  complex  protein  molecules  to  urea 
is  certain, 

A  faulty  metabolism,  which  stops  short  of  normal  oxidations, 
results  in  throwing  these  amino  acids  off  in  the  urine  or  feces 
and  their  presence  indicates  abnormal  conditions  of  one  sort 
or  another. 

NH2 

Amino  formic  or  carbamic  acid,  I  ,  is  a  hypothetical 

COOH 


226  ORGANIC   CHEMISTRY 

acid  which  would  consist  simply  of  an  amino  group,  NH2,  united 
to  a  carboxyl  group,  COOH.  By  the  union  of  ammonia  and 
carbon  dioxide  the  ammonium  salt  of  this  acid  is  formed, 

NH2 

2  NH3  +  CO2  =  I 

COONH4 

Ammonium  carbamate  is  a  constituent  of  commercial  ammo- 
nium carbonate  and  an  antecedent  of  ammonium  carbonate  in 
the  hydrolysis  of  urea. 

Amino-acetic  Acid,  also  called  glycocoll  and  glycin,  is  ob- 
tained with  other  amino  acids  by  boiling  glue  with  either  acids 
or  alkahes.*  It  is  also  obtained,  by  the  hydrolysis  of  glycochoKc 
acid,  from  bile. 

Hippuric  Acid  (Plate  V,  Fig.  4)  consists  of  benzoic  acid 
united  chemically  to  glycocoll,  and  may  be  produced  syntheti- 
cally by  the  union  of  these  two  substances. 

Amino-Valeric  Acid,  CH2(XH2)-(CH)3-C200H,  may  be 
obtained  ^\dth  glycocoll  from  elastin,  the  protein  of  the  elastic 
fibers,  of  tendons,  etc.f  Isomeric  with  amino-caproic  acid  is 
leucin,  an  amino-isobutyl-acetic  acid. 

""  CH  -  CH2  -  CH(NH2)  -  COOH. 


CH3 


/ 


Leucin,  (CH3)2CH.CH2.CHNH2.COOH,  is  an  a-amino-iso- 

butyl-acetic  acid  and  occurs,  usually  with  tryosin,  as  a  decom- 
position product  of  the  proteins,  including  keratin  and  collagen. 
It  results  from  the  tryptic  digestion  of  the  hemipeptones  and  is 
regarded  with  other  amino  acids  as  among  the  antecedents  of 
urea.  Leucin  only  rarely  occurs  in  the  urine.  WTien  pure  it 
crystallizes  in  thin,  hexagonal  plates,  but  as  found  in  urine  it  is 
usually  in  the  form  of  "  spheres "  represented  by  Fig.  2  of 
Plate  V. 

*  Bemthsen,  Organic  Chemistry. 

t  Foster,  Chemical  Basis  of  the  Animal  Body. 


ORGANIC  ACIDS  227 

Cystin,  C6Hi2N2S204,  is  an  amino  acid  occasionally  found  in 
the  urine  in  diseases  where  the  sulphur  compounds  fail  to  be 
properly  oxidized.  It  occurs  under  these  circumstances  as  reg- 
ular colorless  hexagonal  plates  (Plate  X,  Fig.  6). 

By  the- oxidation  of  cystin  and  subsequent  splitting  off  of 
carbon  dioxide  taurine  is  produced.  For  occurrence  of  taurine 
see  page  232. 

Tyrosin  is  a  complex  amino  acid  obtained  from  the  decom- 
position of  protein  substances,  particularly  old  cheese.  It  is  oc- 
casionally found  in  urinary  sediments  as  colorless  needle-shaped 
crystals  usually  grouped  as  tufts  or  "  sheaves"  (Plate  V, 
Fig.  6). 

Dibasic  Amino  Acids. 

Of  this  class  of  compounds  two  may  be  mentioned:  amino- 
succinic,  aspartic  or  asparaginic  acid,  COOH  —  CH2  —  CH(NH2)  — 
COOH,  may  be  obtained  from  animal  and  vegetable  proteins 
and  in  the  pancreatic  digestion  of  fibrin. 

Glutamic  Acid  is  an  amino-glutaric  (pyrotartaric)  acid,  and 
occurs  similarly  to  aspartic  acid,  except  that  it  is  not  formed  by 
pancreatic  digestion. 


CHAPTER  XXV. 
CYANOGEN   COMPOUNDS.     SULPHUR  COMPOUNDS. 

Cyanogen,  C2N2,  is  an  intensely  poisonous  gas,  colorless, 
heavy  (specific  gravity  1.81),  and  inflammable.  It  is  very 
easily  soluble  in  water  or  alcohol,  forming  unstable  solutions, 
•which,  upon  decomposition,  give  rise  to  various  nitrogen  com- 
pounds,  among  them  ammonia,  hydrocyanic   acid,   and  urea. 

Cyanogen  may  be  prepared  by  heating  the  cyanides  of 
silver,  mercury,  or  gold,  or  by  the  dry  distillation  of  ammonium 
oxalate. 

Hydrocyanic  Acid,  HCN,  may  be  produced  by  the  fer- 
mentation of  the  glucoside  amygdahn  from  bitter  almonds; 
also  from  the  kernel  of  peach-stones,  cherry-laurel  leaves,  etc. 
Hydrocyanic  acid  may  be  formed  by  direct  synthesis  of  C2H2 
(acetylene)  and  nitrogen.  The  synthesis  is  induced  by  passing 
electric  sparks  through  the  mixed  gases.  It  is  conveniently 
prepared  in  the  laboratory  by  distilhng  a  mixture  of  dilute  sul- 
phuric acid  with  potassium  ferrocyanide,  K4Fe(CN)6  +  5  H2SO4 
=  6  HCN  -1-  FeSOi  +  4  KHSO4.  Hydrocyanic  acid  is  a  color- 
less, poisonous  liquid,  boiling  at  26.5°  C,  with  a  characteristic 
odor  often  designated  as  a  peach-stone  odor.  It  is  soluble  in 
water  and  a  two  per  cent,  aqueous  solution  constitutes  the  acidum 
hydrocyanicum  dilutum  of  the  pharmacopoeia,  also  known  as 
prussic  acid. 

Potassium  Cyanide  (KCN  or  KCy)  occurs  in  trade  as  a 
white  soHd,  sometimes  granular,  more  often  as  a  powder.  It  is 
intensely  poisonous  owing  to  the  dissociation  of  the  salt  and 
activity  of  the  free  cyanogen. 

228 


CYANOGEN  COMPOUNDS.      SULPHUR  COMPOUNDS         229 

Potassium  cyanide  is  decomposed  by  carbonic  acid  of  the 
air  with  liberation  of  hydrocyanic  acid.  The  aqueous  solution 
of  potassium  cyanide  hydrolyzes  in  two  distinct  ways :  the  most 
easily  apparent  at  ordinary  temperature  is  with  the  formation 
of  hydrocyanic  acid  and  potassium  hydroxide  giving  the  solu- 
tion an  alkaline  reaction: 

KCN  +  H2O  =  HCN  -f  KOH. 

Upon  boiling  a  solution,  the  second  hydrolysis  may  be 
demonstrated  whereby  ammonia  and  potassium  formate  are 
produced : 

KCN  +  2  H2O  =  HCOOK  +  NH3  (Exp.  119). 

The  organic  cyanides  are  known  as  nitrils  or  isonitrils,  accord- 
ing as  the  hydrocarbon  radical  is  attached  directly  to  the  carbon 
or  to  the  nitrogen  of  the  cyanogen  group.  That  is,  methyl 
cyanide  would  be  represented  by  CH3  —  CN,  while  the  isocyanide 
would  be  CH3— NC  (methyl  carbamine);  the  nitrogen  atom 
being  in  the  first  place  trivalent,  in  the  second  quinquivalent. 

Of  these  two  classes  of  compounds,  the  isocyanides  are  of 
much  greater  interest  to  the  student  of  dental  medicine  owing 
to  their  relation  to  the  isocyanates  and  to  urea. 

Phenyl-isocyanide,  CeHsNC,  also  known  as  isobenzonitril, 
is  produced  by  warming  aniline  (C6H5NH2)  with  alcoholic  potash 
and  chloroform,  the  intensely  disagreeable  odor  of  which  is 
utilized  as  a  test  for  chloroform  or  chloral  hydrate  (page  176); 
or,  with  chloroform  and  potassium  hydrate,  the  production  of 
this  isocyanide  may  become  a  test  for  aniline,  acetanilide  (an- 
tifebrin),  and  other  derivatives  of  aniline. 

Potassium  Ferrocyanide,  yellow  prussiate  of  potassium, 
K4Fe(CN)6,  is  obtained  by  heating  animal  refuse  with  a  little 
over  one- third  its  weight  of  potassium  carbonate  and  scrap 
iron.  The  mixture  is  covered  so  as  to  exclude  the  air  and  after 
cooling  the  resulting  mass  is  boiled  with  water  and  filtered. 


230 


ORGANIC  CHEMISTRY 


Upon  evaporation  of  the  filtrate  potassium  ferrocyanide  will 
separate  as  yellow,  four-sided  crystals  with  a  formula  K4Fe(CN)6. 
3  H2O.  The  complex  acid  ion  (Fe(CN)6)  is  not  regarded  as 
poisonous  but  can  be  made  to  dissociate  by  the  addition  of  acid. 
See  Exp.  122.  By  the  action  of  strong  sulphuric  acid  the  radical 
is  broken  up  and  carbon  monoxide  is  evolved.  Dilute  sulphuric 
acid  will  yield  hydrocyanic  acid  according  to  the  reaction  on 
page  228. 

PotassiumFerricyanide,  redprussiate  of  potassium,  K3Fe(CN)6, 
contains  iron  in  the  ferric  condition  and  may  be  made  by  oxidiz- 
ing the  ferrocyanide  by  the  action  of  chlorine  gas. 

Cyanic  Acid,  HCNO,  may  be  made  by  distillation  of  its 
polymer,  cyanuric  acid  (HCN0)3.  Cyanic  acid  cannot  be  made 
in  the  usual  way  by  decomposition  of  its  salts  with  mineral  acids, 
since  in  the  presence  of  water  cyanic  acid  becomes  ammonium 
carbonate. 

Potassium  cyanate  may  be  prepared  by  direct  oxidation  of 
potassium  cyanide  with  lead  oxide. 

Ammonium  cyanate  passes,  upon  heating,  directly  into 
urea.     See  Exp.  126. 

Isocyanic  Acid,  0  =  C  =  N-H  (carbimide)  is  supposed  to  be 
the  acid  of  ordinary  potassium  and  ammonium  cyanates. 

Fulminic  acid  (C  ^  N-O-H),  isomeric  with  cyanic  acid 
N  =  C-O-H  and  isocyanic  acid  (O  =  C  =  N-H),  is  im- 
portant only  because  of  its  relation  to  the  fulminates,  which  are 
explosive  compounds  of  the  acid,  with  some  of  the  heavy  metals, 
such  as  silver  and  mercury. 

Thiocyanic  Acid  or  Sulphocyanic  Acid.  —  In  this  acid  and 
its  salts,  the  atom  of  sulphur  replaces  the  oxygen  of  cyanic  acid 
in  the  empirical  symbol  (HCNS) ;  but,  graphically,  the  sulphur 
is  attached  to  the  basic  element  (metal  or  hydrogen)  rather  than 
to  carbon:  thus,  K-S-C  -  N,  that  is,  the  sulphocyanate  is 
not  an  isocompound.  For  occurrence  and  relations  of  HCNS  in 
the  human  body,  see  chapter  on  Saliva. 


cyanogen  compounds.    sulphur  compounds       23 1 

Sulphur  Compounds. 

Mercaptan,  an  organic  sulphhydrate.  The  name  mercaptan 
comes  from  two  Latin  words  signifying  ''taking  mercury" 
(mercurium  cap  tans),  because  of  compounds  readily  formed  with 
mercuric  oxide.  Representatives  of  this  class  of  compounds  are 
found  as  derivatives  of  both  the  open  and  the  closed-chain 
hydrocarbons. 

Ethyl  mercaptan,  thioalcohol,  C2H5SH,  is  a  type  of  this  class. 
It  is  a  colorless  liquid,  with  bad  odor,  slightly  soluble  in  water, 
boils  at  37°  C,  and  is  used  in  the  preparation  of  sulphonal. 

The  mercaptans  may  be  prepared  by  action  of  KHS  on  the 
alkyl  haloids: 

C2H5I  +  KHS  =  C2H5SH  +  KI. 

The  thioalcohols  form  potassium  and  sodium  compounds 
similar  to  common  alcohol, 

C2H5SH  +  K  =  C2H5SK  +  H. 

Mercaptol,  a  name  which  has  been  applied  to  the  thioketones. 
The  simple  compounds  of  this  class  are  not  known  as  they  form 
polymers  very  readily.  A  dimethyl-diethyl  compound  is  pro- 
duced in  the  process  for  preparation  of  sulphonal. 

Thioethers  are  organic  sulphides  prepared  in  a  manner 
analogous  to  that  employed  in  the  preparation  of  the  thio- 
alcohols, the  inorganic  sulphide  being  used  in  place  of  the  sulph- 
hydrate, for  example:    2  C2H5Br  +  K2S  =  (C2H5)2  S  +  2  KBr. 

Sulphones  are  oxidation  products  of  organic  sulphides:  as, 

for  example,  ethyl  sulphone  ^  S  :^    . 

C2H5/    '^O 

Sulphonal  is  a  derivative  of  mercaptan  as  previously  stated. 

It  may  be  prepared  by  the  action  of  acetone  and  ethyl  mercaptan 

with  hydrochloric  acid  and  subsequent  oxidation  of  the  resulting 

product. 


232  ORGANIC   CHEMISTRY 

Sulphonic  Acids  as  a  class  may  be  obtained  by  the  oxidation 
of  an  organic  sulphhydrate  (mercaptan).  This  oxidation  may  be 
produced  by  the  action  of  nitric  acid  or  potassium  permanganate, 
and  may  be  written  as  follows: 

C2H5SH  +  30  =  C2H5.SO2.HO. 

Taurine  is  an  important  sulphonic  acid  of  the  paraffin 
series.     Its  graphic  formula  shows  it  to  be  an  amino  ethyl  sul- 

,      .        .  /HSO3 

phonic  acid,  C2H4  .     Taurine  is  derived  from  taurocholic 

^NHo 

acid  by  hydrolysis.     This  acid  is  representative  of  one  of  the  two 

principal  acid  groups  occurring  in  the  bile,  the  salts  of  which  may 

be  found  in  pathologic  conditions  in  the  urine,  or,  according  to 

Dr.  J.  P.  Michaels  and  others,  in  the  saUva. 


CHAPTER  XXVI. 
AMINES   OR   SUBSTITUTED   AMMONIAS. 

If  one  or  more  of  the  hydrogen  atoms  of  ammonia,  NH3,  be 
replaced  by  a  hydrocarbon  group,  the  resulting  compound  is  an 
amine;  thus  CH3  — NH2  is  methylamine,  and  (CH3)2NH  is  di- 
methylamine.  Trimethylamine,  (CH3)3N,  has  been  found  among 
the  decomposition  products  of  fresh  brain,  human  Hver,  and 
spleen.* 

When  one  hydrogen  atom  only  has  been  substituted  in  NH3 
the  amine  is  known  as  a  primary  amine  or  amino  compound 
(containing  the  NH2  group) .  These  may  be  prepared  in  a  num- 
ber of  ways,  two  of  which  we  will  consider.     . 

If  alkyl  iodides  or  bromides  are  heated  with  alcoholic  am- 
monia, compounds  are  produced  analogous  in  composition  to 
the  ordinary  ammonium  salts: 

CH3I  +  NH3  =  NH2CH3.HI. 

Upon  distilling  the  methyl  ammonium  iodide  (of  this  reaction) 
with  caustic  alkali  the  amine  results: 

NH2CH3HI  +  KOH  =  NH2CH3  +  KI  +  HoO. 

The  second  method  is  by  the  action  of  nascent  hydrogen 
upon  alcoholic  solution  of  the  nitrils: 

CH3CN  +  2  H2  =  C2H5NH2. 

The  disagreeable  odor  of  carbylamine  constitutes  a  char- 
acteristic test  for  the  primary  amines.  This  is  known  as  Hof- 
mann's  Carbylamine  Reaction  and  may  be  easily  brought  about 

*  Vaughn  and  Nov}',  Cellular  Toxins. 
233 


234  ORGANIC  CHEMISTRY 

by  warming  the  amine  with  a  Httle  chloroform  and  alcoholic 
potash. 

The  secondary  amines  are  those  in  which  two  hydrogen 
atoms  of  ammonia  have  been  replaced  as  in  dimethyl  amine 
(CH3)2NH.  These  compounds  have  also  been  called  imines 
(imides)  or  imino  (imido)  compounds  because  they  contain  the 
"imino"  group  (NH). 

Imides  are  formed  with  a  number  of  the  dibasic  organic 
acids.  The  one  of  greatest  interest  is  perhaps  the  imide  of 
succinic  acid  which  may  be  produced  by  the  following  reaction. 
Ammonium  succinate  subjected  to  heat  splits  off  2  H2O  +  NH3, 

CH2.C0\ 
becoming   I  NH,      The  hydrogen   of  the  imide  group 

CH2.CO/ 
may  be  replaced  by  metals  such  as  potassium,  silver,  or  mercury. 
Succinimide  may  also  be  produced  by  heating  succinic  acid, 
carbonic  anhydride,  and  ammonia.  This  with  mercuric  oxide 
will  give  a  white  powder  soluble  in  water,  which  is  the  mercuric 
succinimide  largely  used  for  the  treatment  of  pyorrhea. 

The  secondary  amines  may  be  produced  by  further  action 
of  alkyl  iodides  and  the  primary  amines.  By  action  of  sodium 
nitrite  and  hydrochloric  acid  upon  fairly  strong  solution  of  a 
secondary  amine  a  nitrosamine  is  formed  which,  when  mixed 
with  phenol  and  strong  sulphuric  acid,  gives  a  dark  green  solu- 
tion which  becomes  red  upon  dilution  with  water  and  this  in  turn 
becomes  blue  or  green  upon  neutralization  with  a  fixed  alkali. 

Trimethyl  amine  formed  with  the  methyl  and  dimethyl 
amines  is  a  liquid  with  a  not  unpleasant  odor. 

Diamines  are  derived  from  two  molecules  of  ammonia,  as 

/  NH2 
ethylene  diamine,  C2H4 , 

^NH2 

To  this  class  of  compounds  belong  many  of  the  "ptomaines," 

produced  by  the  putrefaction  of  organic  matter,  as  putrescine 

(butylene  diamine),  CH2NH2  — (CH2)2  — CH2NH2,  and  cadaver- 


AMINES  OR   SUBSTITUTED   AMMONIAS  235 

ine  (penta-methylene  diamine),  CH2NH2  — (CH2)3  — CH2NH2. 
A  large  number  of  the  ptomaines  are  aromatic  compounds  and  as 
such  will  be  referred  to  later. 

Amides. 

If  the  hydrogen  of  ammonia  be  replaced  by  an  oxygenated  or 
acid  radical,  an  amide  results;  thus  NH2(C2H30)  is  acetamide, 
or  this  compound  may  be  regarded  as  acetic  acid,  CHg  —  COOH, 
in  which  the  OH  has  been  replaced  by  NH2. 

It  may  be  easier  for  the  student  to  remember  an  amide  as  an 
organic  acid  with  the  OH  of  its  carboxyl  replaced  by  the  "  amido  " 
or  amino  group  NH2. 

Acetamide  may  be  prepared  by  the  action  of  strong  am- 
monia upon  ethyl  acetate : 

CH3COOC2H5  +  NH3  =  CH3CONH2  +  C2H5OH. 

It  forms  colorless  crystals  soluble  in  both  alcohol  and  water. 

Cyanamide  (NH2  in  place  of  the  hydroxyl  of  cyanic  acid), 
NCNH2,  is  prepared  by  the  action  of  ammonia  on  cyanogen 
chloride.  The  calcium  compound  is  of  commercial  importance 
as  a  means  of  utilizing  atmospheric  njtrogen  for  agricultural 
purposes.  CaC2  heated  with  N2  becomes  NCNGa;  this  in  a 
crude  state  is  used  as  fertilizer.  The  calcium  cyanamide  by 
action  of  carbon  dioxide,  water,  and  soil  bacteria  becomes  first 
urea,  then  ammonium  carbonate.     See  page  237. 

Formamide,  CHO.NH2,  is  a  liquid  miscible  with  both  alcohol 
and  water.  It  boils  with  partial  decomposition  at  about  200°  C. 
Upon  heating  quickly,  it  splits  into  carbon  monoxide  and  am- 
monia.    (Bernthsen.) 

Phenyl-formamide,  CHO.NHCeHs,  known  as  formanilide, 
occurs  as  yellow  crystals  soluble  in  water  and  in  alcohol. 

Hydrazines. 
From  diamide,  NH2— NH2,  or  hydrazine,  may  be  derived  such 
substitution  products   as  methyl-hydrazine,   CH3— NH— NH2; 


236  ORGANIC  CHEMISTRY 

ethyl-hydrazine,      C2H5-NH-NH2;      and     phenyl-hydrazine, 
C6H5NH-NH2. 

This  latter  compound  forms,  with  the  monosaccharids  and 
with  many  of  the  disaccharids,  yellow  crystalline  compounds, 
known  as  osazones,  which  are  precipitated  in  characteristic 
crystalline  forms,  recognizable  upon  microscopical  examination 
and  by  their  melting-points  (see  under  Carbohydrates,  page  261). 


CHAPTER  XXVII. 
UREA   AND   URIC   ACID. 

This  substance  forms  about  50%  of  the  total  solids  and 
about  85%  of  the  nitrogenous  matter  contained  in  the  urine. 
When  we  consider  that  only  5%  of  the  nitrogenous  waste  passes 
ofT  in  the  feces  and  95%  in  the  urine,  the  importance  of  urea  as 
an  index  of  the  nitrogen  excreted  and  of  protein  metabolism 
becomes  apparent. 

Urea  was  the  first  organic  substance  synthesized  from  in- 
organic compounds.  This  was  accomplished  by  producing  a 
molecular  rearrangement  of  ammonium  isocyanate.  The  reaction 
is  conveniently  brought  about  by  the  double  decomposition  of 
potassium  cyanate  and  ammonium  sulphate  and  subsequent 
evaporation  of  the  solution  to  dryness: 

2  CNOK  +  (NH4)2S04  =  2  OCN.NH4  +  K2SO4. 

Then   O  =  C  =  N  —  NH4    (ammonium   isocyanate)  +  heat  = 

/NH2 

O  =  C,  (urea). 

^NH2 

OTT 
Urea  is  the  amide  of  carbonic  acid,  O  =  C  ^       ,  and  from 

this  type  may  be  explained  the  rapid  transformation  of  urea  into 

.  ,  .  ,        .  /NH2 

ammomum  carbonate  m  stale  urme.     O  =  C  with  one 

,      1  /ONH4 

molecule  of  H2O  becomes  O  =  C ,  or  ammonium  carba- 

^NH2 

mate,  and  this,  by  addition  of  a  second  molecule  of  water,  be- 

237 


238  ORGANIC  CHEMISTRY 

/ONH4 
comes    O  =  C ,  or   ammonium    carbonate,    (NH4)2C03. 

^0NH4 

The  last  part  of  the  reaction  takes  place  whenever  commercial 
"ammonium  carbonate"  [really  a  mixture  of  carbamate 
(NH4-NH2-CO2)  and  acid  carbonate  (NH4HCO3)]  is  dissolved 
in  water. 

Urea  crystallizes  in  long  needle-shaped  crystals  of  the  rhom- 
bic system.  It  is  insoluble  in  water,  somewhat  soluble  in 
alcohol,  and  nearly  insoluble  in  ether.  It  fuses  at  132°,  and  at 
a  somewhat  higher  temperature  it  gives  off  ammonia  and  am- 
monium carbonate,  and  at  160°  leaves  a  residue  of  ammelide, 
cyanuric  acid,  and  biuret.  Urea  is  decomposed  by  solutions  of 
the  alkaline  hypochlorites  or  hypobromites,  being  broken  up  into 
N,  CO2,  and  H2O,  as  follows: 

COCNHo)"  +  3  NaOBr  =  CO2  +  N2  +  2  H2O  +  3  NaBr. 

Cyanuric   Acid,    N3C3O3H3,    is   a   polymer    of    cyanic    acid 

(NCOH),  which  is,  at  first,  formed  in  the  above  decomposition. 

/CO  -  NH2 
Biuret,  H—  Nf  ,  may  be  obtained  by  heatmg 

^  CO  -  NH2 

urea.     When  pure,  it  occurs  as  white,  needle-shaped  crystals. 

With  NaOH  and  1%  CUSO4  it  gives  the  characteristic  violet  and 

rose-red  shades  obtained  in  the  biuret  reaction  (Piotrowski's 

protein  test).     Exp.  189,  page  406. 

Urea  Nitrate  may  be  precipitated  from  fairly  concentrated 
urine  by  addition  of  HNO3.  It  separates  in  hexagonal  crystals 
or  plates,  easily  recognizable  under  the  microscope  (Plate  V, 
Fig.  3,  opposite  page  204).  . 

Urea  Oxalate,  —  Upon  addition  of  a  solution  of  oxalic  acid 
to  concentrated  urine,  crystals  of  oxalate  of  urea  are  precipi- 
tated. They  are  rather  more  easily  obtained  in  characteristic 
forms  (Plate  II,  Fig.  5,  opposite  page  170)  than  are  the  crystals 
of  nitrate,  and,  in  consequence,  treatment  with  oxalic  acid  con- 
stitutes a  better  method  for  the  quaHtative  detection  of  urea  in 


URFA   AND    URIC   ACID  239 

the  body  fluids  than  the  nitric  acid  test  formerly  used.     These 

crystals  polarize  Hght,  and  the  use  of  the  micropolariscope  faciU- 

tates  their  detection. 

Substituted   Ureas.  —  The   hydrogen   of    the   amino    group 

may  be  replaced  by  alcohol  radicals  forming  what  are  known 

/NH2 
as   alkylated   ureas;    thus,   O  =  C^  is    methyl    urea, 

^NHCHs 

IV  TT 

O  =  C  '^  ,  ethyl  urea,  and  one,  two,  three,  or  all  four 

^NHCsHs 

of  the  hydrogen  atoms  may  be  so  replaced. 

When,  in  place  of  an  alcohol  radical,  the  acid  radical  is  in- 
troduced, a  class  of  compounds  known  as  "ureides"  results;  thus 

/NH2 

^NHCCaHgO)  (acetyl  urea). 

COOH 

In  a  case  of  a  dibasic  acid,  such  as  oxalic,  I  ,  entering 

COOH 
into  the  reaction,  one  or  both  (OH)  groups  may  be  split  off,  form- 

/NH2 

ing  in  the  first  instance  a  ureide  acid,  as  O  =  C ,  > 

^NH.CO.COOH 

oxaluric  acid, 

COOH  /NH2  /NH2 

I  +0  =  C  =0  =  C  +  H2O, 

COOH  ^NHa  ^NH-CO 

I 
COOH 

/NH-C=0 
or,  in  the  second  case,  a  ureide,  as  O  =  C  I       parabanic 

^NH-C=0 
acid. 

If  the  residue  of  two  molecules  of  urea  enter  into  the  composi- 
tion of  the  hew  molecule,  the  compound  is  a  diureide.  Of  this 
class  one  of  the  most  important  is : 


240  ORGANIC  CHEMISTRY 

Uric  Acid,  trioxypurin,  C5H4N4O3.     Its  relation  to  urea  may 

NH-CO 
I        I 
be  shown  by  the  graphic  formula  O  =  C       C— NH\ 

I        II  C  =  O. 

NH-C-NR/ 
Uric  acid  is  also  referable  to  a  purely  h3^othetical  base,  "purin," 
by  the  use  of  which  the  relationship  of  xanthin,  hypoxanthin, 
and  other  "purin"  or  nuclein  bases  is  easily  demonstrated. 

These  bases  are  of  great  physiological  interest,  in  that  they 
form  an  unquestioned  link  between  the  decomposition  products 
of  the  proteins,  nuclein,  etc.,  on  the  one  hand,  and  uric  acid 
and  the  urates  on  the  other. 

Uric  acid  normally  occurs  in  the  urine  combined  with  alkaline 
bases,  also  with  traces  of  calcium  and  magnesium.  It  is  insoluble 
in  alcohol,  ether,  or  dilute  acids;  practically  insoluble  in  water, 
but  much  more  soluble  in  solutions  of  urea  or  of  glycerin.  A 
solution  of  uric  acid  does  not  redden  blue  litmus. 

Purin  is  represented  by  the  formula  C5H4N4,  or  graphically 
N  =  C-H 

I  I 

as  H  —  C     C  —  N  —  H        .     If  we  now  break  all  double  bonds  ex- 

II  II         ^C-H 
N-C-N 

cept  those  Hnking  two  carbon  atoms  (4  and  5),  we  obtain  a 
I  -  N-C6 
I       I 
graphic  nucleus,  2  =  C     C^  — N  — 7        ,  by  numbering  the  atoms 
I       II  )C=8 

3  -N-C4-N-9 
of  which  we  may  easily  designate  any  structural  formula  of  the 
group;    thus,  2  —  6  —  8,  trioxypurin,  is  uric  acid  as  above,  while 

H-N-C=0 
I       I 
xanthin  is  2  —  6,  dioxypurin,  O  =  C     C  — N  — H       ,andi— 3  — 7, 

I      II         )C-H 
H-N-C-N^ 


URFA    AND    URIC   ACID  241 

CH,-N-C  =  0 

I       I 
trimethyl-xanthin,  O  =  C     C  —  N  — CH3  ,  is  caffein  and  thein, 

I       II  iC-H 

CH3-N-C-N 
alkaloids  from  coffee  and  tea. 

Traces  of  xanthin  (2.6  dioxypurin),  hypoxanthin  (6  oxy- 
purin),  guanin  (2  imino,  6  oxypurin),  adenin  (6  amino  purin), 
and  heteroxanthin  (7  methyl  xanthin)  have  been  found  in  urine, 
and,  in  cases  of  leukemia,  many  of  them  in  increased  amounts, 
notably  xanthin,  hypoxanthin,  and  adenin  (Witthaus). 

Uric  acid  occurs  in  the  urine;  there  are  traces  of  it  in  the 
blood;  and  it  is  occasionally  found,  in  the  form  of  urates,  in  saliva. 
It  is  a  dibasic  crystalline  acid,  colorless  when  pure;  but,  in  uri- 
nary sediment,  it  occurs  generally  as  crystals,  yellow  to  red, 
''whetstone "-shaped,  and  in  various  other  forms  (Plate  X,  Figs. 
I  and  2).  The  "brickdust"  deposit  occasionally  found  in  urine 
consists  of  uric  acid.  It  is  insoluble  in  alcohol  and  nearly 
insoluble  in  water ;  but  its  solubility  in  water  is  increased  by  the 
presence  of  urea. 

Upon  heating  uric  acid,  urea  and  cyanuric  acid  may  be  ob- 
tained; NH3  and  CO2  are  given  off.  We  are  not  to  infer  from 
this  decomposition  that  the  uric  acid  is  an  antecedent  of  urea 
in  the  animal  body;  for  such  is  not  the  case,  except  possibly 
to  a  limited  extent. 

Uric  acid  produces,  upon  oxidation,  a  variety  of  compounds, 
according  to  the  temperature  and  the  oxidizing  agent  employed. 

Chlorine,  hot,  yields  cyanuric  acid,  C3N3(OH)3.     Chlorine  or 

/       /NHCO.        \ 
bromine,  cold,  forms  oxalic  acid,  alloxan  ICO,  .CO), 

,  \       ^NHCO^      / 

"  /      ./NH-CO\ 

parabanic    acid    I  CO .  I     I    and    ammonium    cyanate. 

\  NH-CO/ 

HNO3  in  the  cold,  forms  alloxan,  alloxan  tin,  and  urea  (Witthaus). 


242  ORGANIC  CHEMISTRY 

Uric  acid  may  be  detected  by  the  murexide*  test.     See  Exp. 

131.  page  394- 

While  uric  acid  is  practically  insoluble  in  H2O  and  the  acid 
urates  only  sparingly  soluble,  the  uric  acid  in  the  system  is 
apparently  held  in  solution  as  an  acid  urate  (NaHU)  by  the 
presence  of  the  sodium  phosphates,  NaH2P04  and  Na2HP04, 
possibly  also  aided  by  the  presence  of  some  unknown  organic 
combination. 

NaHU  +  NaH2P04  forms,  at  38°  C,  a  solution  with  an  acid 
reaction;  if,  however,  the  mixture  is  cooled  to  room  tempera- 
ture, the  reaction  becomes  alkaline  from  Na2HP04,  and  uric 
acid  is  precipitated  (Bunge) : 

NaHU  +  NaH2P04  =  Na2HP04  +  H2U. 

Na2HP04  is  a  normal  constituent  of  the  blood,  and  a  tendency 
to  precipitate  uric  acid  may  be  met  by_the  following  reac- 
tion: Na2HP04  -\-  HaU  =  NaH2P04  +  NaHU.  Because  the  acid 
urate  of  lithium  is  much  more  soluble  in  water  than  any  of  the 
other  monometalUc  urates,  lithium  salts  have  long  been  used  as 
uric  acid  solvents.  But  the  fact  that  lithium  solutions  will 
precipitate  from  solutions  of  Na2HP04  crystals  of  Li2HP04,  has 
been  made  the  basis  for  a  claim  that  such  use  of  lithium  salts  is 
without  effect  other  than  to  decompose  and  render  insoluble 
the  alkaline  phosphate,  which  has  been  acknowledged  a  valu- 
able factor  in  keeping  uric  acid  in  solution.  While  the  disodic 
phosphate  is  regarded  by  many  as  superior  to  lithium  salts  as 
a  uric  acid  solvent,  the  fact  of  comparative  insolubility  of 
Li2HP04  can  hardly  be  regarded  as  conclusive  evidence  that 
lithium  compounds  are  not  effective. 

The  following  in  regard  to  our  need  for  "  sarsaparilla "  in 
the  spring  is  given  by  Dr.  E.  C.  Hill,  of  the  University  of  Den- 
ver, in  his  text-book  of  chemistry,  page  370:    "Reduced  alka- 

*  Note.  —  Murexide  is  a  definite  chemical  compound  (CsHjNfiOe)  and  may  be 
produced  from  alloxantin;  an  oxidation  product  noted  above. 


UREA    AND   URIC   ACID  243 

linity  of  the  blood,  as  in  winter  from  eating  meats  freely,  throws 
uric  acid  out  of  solution  to  collect  in  the  more  acid  tissues  (spleen, 
liver,  and  joints).  With  the  vernal  tide  of  alkalinity  (due  to 
freer  sweating,  with  excretion  of  fatty  acids)  these  deposits  are 
swept  out  in  the  blood-current,  irritating  the  nerves  and  giving 
rise  to  'that  tired  feeling.'" 


CHAPTER  XXVIII. 
CLOSED-CHAIN   HYDROCARBONS. 

In  illustrating  the  simpler  relationship  of  organic  compounds 
we  have,  as  far  as  possible,  carefully  avoided  reference  to  the 
closed-chain  or  aromatic  compounds,  as  the  characteristic  group- 
ings are  more  easily  seen  by  the  use  of  simple  formulae. .  The 
distinguishing  feature  of  the  aromatic  (also  called  cyclic)  com- 
pounds is  a  nucleus  consisting  of  a  closed  chain  of  atoms;  this 
chain  may  contain  three,  four,  five,  six,  or  seven  members,  but 
the  six-carbon  ring  is  by  far  the  most  important,  and  the  only 
one  which  we  are  to  consider. 

The  hydrocarbons  of  the  aromatic  series  have,  for  a  general 
formula,  C„H2n-6,  the   simplest  being  benzene  or  benzol,  CeHe; 
and  we  may  consider  that  the  aromatic  compounds  are  derived 
from  this.      The  structure  of    the  benzene  molecule  is  repre- 
sented by  Kekule's  benzene  ring.     Note  that  „ 
there  are  three  double  bonds,  which  of  course  | 
permit  of  addition  products,  as  C6H6CI2,  ben-           /r^\ 
zene  di-chloride,  etc.     The  substitution  prod- H  — C        C  — H 
ucts  are,  however,  of  far  greater  importance.               I  II 

Benzene,  CeHe  (benzol),  is  a  colorless  liquid  ^"C  C  — H 
from  the  "light-oil"  obtained  by  distillation  of  C 

coal-tar.     It  boils  at  80°,  has  a  gravity  of  0.899,  ■„. 

is  soluble  in  ether,  alcohol,  and  chloroform,  but 
insoluble  in  water.     It  may  be  made  pure  by  distilling  an  inti- 
mate mixture  of  benzoic  acid  and  quicklime,  and  at  a  temper- 
ature of  about  5°  C.  may  be  obtained  as  a  crystalline  solid, 
CeHsCOOH  -f  CaO  =  CaCOa  +  CeHe.       (See  Exp.   135,  page 

395-) 

244 


CLOSED-CHAIN  HYDROCARBONS  245 

Benzene  may  be  considered  as  phenyl  hydride,  CeHsH,  and 
similarly  to  the  straight  chain  hydrocarbons  two  of  these  phenyl 
groups  may  be  made  to  combine  giving  a  hydrocarbon  Ci2Hio, 
known  as  diphenyl.  Reaction  2  CeHsBr  +2  Na  =  C12H10  + 
2  NaBr. 

Toluene,  (toluol).  —  The  next  higher  homologue  of  the  series 
will  be  CtHs;  this  is  methyl  benzene  (CeHsCHs)  or  toluene. 

The  hydrocarbons  of  this  series  may  be  prepared  in  a  manner 
similar  to  that  used  in  the  preparation  of  the  hydrocarbons  of 
the  paraffin  series. 

Toluene  may  be  made  by  the  action  of  metallic  sodium  upon 
a  mixture  of  brombenzene  and  methyl  iodide. 

CeHsBr  +  CH3I  +  Na2  =  CeHsCHa  +  NaBr  +  Nal. 

Toluene  is  a  colorless  liquid  boiling  at  110°  C,  and  yielding 
upon  oxidation  a  benzene  derivative;  i.e.,  the  CH3,  or  so-called 
side  chain,  is  the  part  of  the  compound  changed  by  ^oxidizing 
agents  rather  than  the  benzene  ring, 

C6H5CH3  +  30  =  C6H5CO2H  +  H2O. 

Xylene,  CsHio  (xylol)  or  dimethylbenzene,  the  next  hydro- 
carbon of  this  series,  exists  in  coal  tar  as  a  mixture  of  three 
isomeric  compounds  which  may  be  graphically  represented  as 
follows : 

CH3  CH3  CH3 

0^  n 


^-u-  and 


These  three  possible  positions  of  the  second  substitution  are 
known  as  ortho-,  meta-,  and  para-;  thus,  the  first  representation 
at  the  left  will  be  ortho-xylene,  or  ortho-dimethylbenzene.  The 
other  two  will  be  meta-xylene  and  para-xylene  respectively. 

A  trisubstituted  benzene  may  be  "adjacent,"  if  the  sub- 
stituted element  or  group  is   attached   to   the   carbon  atoms 


246  ORGANIC  CHEMISTRY 

1  —  2  —  3,    or    " unsymmetrical "     1  —  2—4,    or    "symmetrical" 

1-3-5- 

A   fourth   isomer   of   dimethylbenzene   would   be    an   ethyl 

benzene,  C6H5C2H5.     This,  upon  oxidation,  yields  benzoic  acid, 

in  a  manner  similar  to  toluene.     (Bernthsen.) 

Mesitylene,  C9H12,  is  a  trimethylbenzene.     Only  two  isomers 

are  possible.     It  can  be  prepared  by  dehydrating  acetone  by 

the  use  of  sulphuric  acid: 

3C3H60-3H20  =  C9Hi2. 

Hydroxy  Derivatives  of  the  Aromatic  Hydrocarbons. 

Phenol,  carbolic  acid,  or  oxybenzene,  CeCsOH,  obtained 
from  the  distillation  of  coal-tar,  and  used  as  an  antiseptic  and 
disinfectant.  For  properties  and  test,  see  page  183.  Phenol 
acts  like  an  acid,  in  that  it  forms  salts  with  the  metallic  bases, 
CeHsOK,  potassium  phenolate,  but  it  does  not  have  an  acid 
reaction  on  litmus  paper  or  other  indicators,  i.e.,  it  does  not 
have  free  hydrogen  ions  when  in  solution,  but  belongs  to  the 
alcohols  rather  than  the  acids. 

The  three  di-hydroxybenzenes  are  all  of  interest  and  are 
graphically  represented  as  follows: 

OH  OH 

/  \  r^XJ    orlho-dihydroxy        /     \  wjeto-dihydroxy 

I  I  Uirl        benzene  or  |  |  benzene  or 


pyrocatechol  |  /  ^U"      resorcinol 


and 

OH 


/>ara-dihydroxy 
benzene  or 
hydroquinol 


OH 


The  ortho  compound  is  pyrocatechol.  Its  ethereal  sulphate 
(acid  sulphate)  is  given  by  Hoppe-Seyler  as  a  constituent  of  nor- 
mal urine,  and  its  monomethyl  ether,  guaiacol,  C6H4OH  —  O  —  CH3, 


CLOSED-CHAIN   HYDROCARBONS  247 

is  obtained  from  beech-wood  creosote,  of  which  it  constitutes 
the  greater  part  (60  to  90  per  cent  U.  S.  D.).  Guaiacol  and 
various  compounds  produced  from  it  have  been  widely  recom- 
mended for  tubercular  diseases. 

Pyrocatechol  has  been  found  to  be  the  most  practical  reagent 
for  the  detection  of  oxidizing  enzymes  *  in  the  saliva. 

Resorcinol  is  a  white  crysta  line  solid,  becoming  more  or  less 
colored  upon  exposure  to  the  light.  It  melts  at  118°  C,  and, 
in  solution,  gives  a  purple  color  with  ferric  chloride.  Heated 
with  sodium  nitrate,  it  produces  a  substance  known  as  "Lac- 
moid"  which  is  used  to  a  considerable  extent  as  an  indicator. 

The  hydroquinol,  or  hydrochinon,  is  a  white  powder  melt- 
ing at  169°  C,  and  is  largely  used  as  a  photographic  developer. 

Pyrogallol,  or  trihydroxybenzene,  C6H3(OH)3  (1  —  2—3),  ^^Y 
be  made  by  heating  gallic  acid,  and  because  of  this  fact  is  usu- 
ally called  pyrogallic  acid.  It  is  a  white  silky  crystal  which, 
like  hydroquinol,  is  used  as  a  photographic  developer.  Dis- 
solved in  a  solution  of  caustic  potash  it  absorbs  oxygen  to  a 
marked  degree,  and  may  be  used  as  a  reagent  for  the  quantita- 
tive determination  of  oxygen  in  gas  analysis. 

Phloroglucinol  is  another  trihydroxybenzene,  isomeric  with 
pyrogallol  but  with  the  hydroxyl  groups  occupying  positions 
1  —  3  —  5  in  the  ring.     The  formula  is  C6H3(OH)3  (1—3  —  5). 

It  crystallizes  in  rhombic  prisms,  soluble  in  water,  alcohol 
and  ether.  This  is  used  in  physiological  chemistry  as  a  reagent 
with  vanillin  as  a  test  for  free  hydrochloric  acid. 

Thymol  (3  methyl-6  isopropyl-phenol) ,  C6H30H(i)CH3(3)C3H7(6,, 
is  a  solid  of  the  nature  of  camphor,  melting  at  44°  C,  and  is 
obtained  from  various  volatile  oils,  particularly  from  the  oil 
obtained  from  Thymus  Vulgaris.  It  is  very  sparingly  soluble  in 
water.  The  addition  of  a  little  alcohol  increases  the  solubility. 
It  is  largely  used  in  the  preparation  of  antiseptic  dental  prepa- 
rations, mouth  washes,  etc. 

*  Journal  of  the  Allied  Dental  Societies,  Vol.  4,  page  346,     Dec,  1909. 


248  ORGANIC  CHEMISTRY 

Cresol,  C3H4CH3OH,  is  a  hydroxy-toluene.  Three  isomeric 
compounds  of  this  formula  are  obtained  from  the  distillation  of 
coal  tar  between  200°  and  210°  C.  The  ortho  and  para  cresols 
are  solid  at  ordinary  temperatures,  the  ortho  compound  melting 
at  31°  C,  the  para  at  36°  C.  Meta  cresol  is  a  liquid  which  does 
not  solidify  unless  under  extreme  conditions  of  cold  and  pressure. 

The  cresols  are  similar  to  phenol  not  only  in  composition  but 
also  in  physical  and  therapeutic  properties;  hence,  cresol  has  been 
called  cresylic  acid,  just  as  phenol  has  been  called  carbolic  acid. 

A  mixture  of  the  cresols,  said  to  be  composed  of  meta  cresol 
40%,  ortho  35%,  and  para  cresol  25%,  constitutes  the  tricresol 
very  largely  used  in  dentistry  as  a  germicide  and  antiseptic  sim- 
ilar to  carbolic  acid. 

An  emulsion  of  cresol,  obtained  by  the  solution  of  resin  soap 
as  an  emulsifying  agent,  is  known  as  creolin.  Cresol  is  also  a 
constituent  of  the  disinfectant  lysol. 

Tricresol  is  miscible  with  formahn  in  all  proportions,  and  the 
mixture  is  recommended  in  the  treatment  of  root  canals. 


Nitrogen  Derivatives. 

Benzidine,  a  diparadiamino  derivative  of  diphenyl  is  made 
by  the  reduction  of  dinitrophenyl;  is  a  solid  substance  melting 
at  122°  C,  and  is  used  as  a  reagent  in  testing  for  blood. 

Nitro-benzene,  C6H5NO2,  may  be  produced  by  treating  ben- 
zene with  a  mixture  of  nitric  and  sulphuric  acid  at  reduced 
temperature.  (Exp.  137,  page  395.)  It  is  a  yellow,  oily  liquid, 
with  the  odor  of  bitter  almonds,  commercially  known  as  oil  of 
mirbane,  and  used  in  the  manufacture  of  aniline. 

Aniline  or  Amino-benzene,  C6H5NH2.  By  reaction  of  nitro- 
benzene with  nascent  hydrogen,  the  NO2  group  becomes  an  NH2 
group  and  aminobenzene  or  aniline  is  produced.  AniHne,  a  color- 
less Hquid,  also  called  aniline  oil,  is  important  from  a  commercial 
rather  than  from  a  medical  standpoint,  as  it  forms  the  basis  of 


CLOSED-CHAIN  HYDROCARBONS  249 

the  aniline  dyes.  When  pure  it  is  a  colorless  hquid,  but  changes 
quite  rapidly  when  exposed  to  the  light.  It  is  used  in  testing  for 
chloral  and  chloroform.  It  is  slightly  soluble  in  water,  and 
easily  soluble  in  alcohol  and  ether.  At  8°  C.  it  becomes  a  crys- 
talline solid. 

Diphenylamine,  (C6H5)2NH,  is  formed  by  the  substitution  of 
the  phenyl  group  for  one  of  the  amino  hydrogens  of  aniline.  It 
crystalHzes  from  petroleum  ether  in  white  crystals  which  melt 
at  54°  C. 

Acetanilide,  CeHs.NH.COCHs,  also  known  as  antifebrine, 
may  be  produced  by  heating  aniline  and  glacial  acetic  acid, 
crystallizes  in  colorless  plates  which  melt  at  115°  C. 

Amino-phenol  may  be  formed  by  the  reduction  of  nitro- 
phenol  by  the  action  of  nascent  hydrogen  (tin  and  hydrogen 
chloride).  The  para  compound  forms  an  ethyl  ester  which  by 
action  of  glacial  acetic  acid  gives  phenacetine  or  para-acet- 
phenetidine, 

\NH.C0.CH3 

Picric  Acid  is  trinitrophenol,  C6H2.0H.(N02)3.  It  may  be 
formed  by  action  of  strong  nitric  acid,  or  mixture  of  sulphuric 
acid  and  nitric  acid  on  phenol.  It  occurs  as  yellow  plates  slightly 
soluble  in  water,  easily  soluble  in  alcohol  and  ether,  and  is  used 
in  Esbach's  reagent  for  the  estimation  of  albumin  in  urine  and 
as  an  alkaloidal  precipitant. 

Salvarsan,  (606) ,  arsenobenzol,  more  accurately  paradiamino- 
dioxyarsenobenzene  hydrochloride,  is  an  arsenic  derivative  of 
benzene  used  in  medical  practice  as  a  specific  for  syphilis. 

-   Aromatic  Acms  and  Aldehydes. 

Benzoic  Acid,  CeHsCOOH,  was  originally  produced  from  gum 
benzoin,  but  may  be  made  from  hippuric  acid  (q.v.),  which 
(from  urine  of  horses)  formerly  constituted  a  commercial  source. 


250  ORGANIC  CHEMISTRY 

It  is  chiefly  prepared,  however,  from  toluene;  it  crystalHzes 
in  colorless  plates  or  long  prismatic  crystals  (from  solution). 
It  is  sparingly  soluble  in  cold  water,  more  soluble  in  hot  water, 
easily  soluble  in  alcohol.  It  sublimes  and  is  inflammable,  burn- 
ing without  residue. 

Benzoates  of  sodium,  ammonium,  lithium,  and  lime  are  all 
used  in  medicine.  Benzoated  or  benzoinated  lard  is  prepared  by 
digesting  gum  benzoin  in  hot  lard.  This  is  much  used  as  a  base 
for  ointments  and  keeps  well. 

Benzaldehyde,  CeHs  — CHO,  is  a  colorless  hquid,  soluble  in 
alcohol  and  ether,  and  sparingly  soluble  in  water.  The  U.  S.  P. 
oil  of  bitter  almonds  is  practically  benzaldehyde;  it  is  a  volatile 
oil,  very  poisonous,  and  upon  standing  deposits  benzoic  acid 
from  partial  oxidation. 

Salicylic  Acid,  orthohydroxybenzoic  acid,  CeHi  — OH.COOH, 
is  a  white  crystalline  powder,  odorless,  irritating  to  mucous  sur- 
faces, soluble  in  alcohol  and  ether,  and  in  about  450  parts  of 
water  at  15°  C.  (U.  S.  D.).  Salicylic  acid  may  be  made  by 
action  of  carbon  dioxide  on  sodium  phenate  and  subsequent 
decomposition  of  the  sodium  sahcylate.  By  heating  rapidly  the 
acid  may  be  changed  into  phenol  and  carbon  dioxide. 

Acetyl  Salicylic  Acid,  C6H4.C2H3O2.COOH,  known  in  medicine 
as  aspirin,  may  be  obtained  by  heating  salicylic  acid  with  acetyl 
chloride.  It  occurs  as  white  needles  slightly  soluble  in  water, 
soluble  in  alcohol  and  ether.  Aspirin  is  decomposed  in  the 
intestine,  salicylic  acid  appearing  in  the  urine  twenty  to  thirty 
minutes  after  administration  of  aspirin. 

Salicylates  have  been  used  to  considerable  extent  in  various 
uric-acid  diseases.  Methyl  salicylate  constitutes  90%  of  natu- 
ral oil  of  wintergreen  (Gaultheria).  The  alcoholic  solution  is 
essence  of  checkerberry. 

Salol  is  phenylsalicylate,  C6H40H.COO(C6H5),  a  white  crys- 
talline powder,  practically  insoluble  in  water  and  not  decom- 
posed by  the  dilute  acids  of  the  stomach  juices;    but  in  the 


CLOSED-CHAIN   HYDROCARBONS  25 1 

intestine  it  becomes  salicylic  acid  and  phenol,  as  follows: 
C6H4.OH.COOC6H,  +  HoO  =  CcH^OH.COOH  +  CeHsOH. 

Gallic    Acid,    a    trihydroxybenzoic  acid,  C6H2(OH)3COOH, 

(i  :  2  :  3  15),  is  prepared  from  tannic  acid  by  action  of  dilute 
sulphuric  acid,  or  by  oxidation  by  exposure  of  powdered  galls. 
It  forms  slightly  brownish  crystals;  if  pure,  the  crystals  are 
colorless.  At  ordinary  temperatures  one  part  of  acid  is  soluble 
in  about  one  hundred  parts  of  water,  five  parts  of  alcohol  or 
twelve  parts  of  glycerine. 

Tannic  Acid,  or  Tannin,  sometimes  called  di-gallic  acid 
because  its  composition,  C14H10O9,  corresponds  to  two  molecules 
of  gallic  acid  less  one  molecule  of  water,  occurs  in  galls,  in  many 
astringent  drugs  and  bark  from  various  trees,  as  hemlock  and 
oak.  Tannic  acid  causes  dark  colored  precipitate  with  ferric 
chloride,  and  precipitates  gelatin,  albumin  and  starch,  differing 
in  all  of  these  particulars  from  galHc  acid.     (U.  S.  D.) 

Hippuric  Acid,  benzoyl  glycocoll,  C6H5  CO.NH.CH2  — COOH, 
occurs  in  traces .  in  human  urine,  to  a  considerable  extent  in 
the  urine  of  the  herbivora,  but  not  at  all  in  that  of  the  carnivora. 
It  crystallizes  in  prismatic  needles  (Plate  V,  Fig.  4),  often  re- 
sembHng  crystals  of  ammonium  magnesium  phosphate;  but  as 
these  latter  only  occur  in  neutral  or  alkahne  urine  and  hippuric 
acid,  usually  in  acid  urine,  there  is  little  danger  of  confounding 
the  two  substances.  Hippuric  acid  is  hydrolyzed  by  the  urease 
of  fermenting  urine,  forming  benzoic  acid  and  glycocoll  (amino- 
acetic  acid) : 

C6H5CO-NH-CH2-COOH  +  H2O 

=  CgHsCOOH  +  CH2NH2COOH. 

Tryosin,  C6H40H-CH2CH(NH2)-COOH,  may  be  crystal- 
lized as  fine  silky  needles.  It  is  formed  from  protein  substances, 
particularly  casein  and  fibrin,  both  by  the  action  of  proteolytic 
enzymes  and  by  putrefactive  processes.  It  rarely  occurs  in  uri- 
nary sediment;  when  found  it  is  in  bundles  or  sheaves  (Plate  V, 


252  ORGANIC  CHEMISTRY 

Fig.  6,  page  204),  and  is  usually  indicative  of  acute  liver  disease, 

phosphorus  poisoning,  etc. 

/  COOH 
Phthalic  Acid,  C6H4  ,  occurs  in  the  form  of  rhombic 

^COOH 

crystals.     By  heating  phthalic  acid,  phthalic  anhydride  may  be 

obtained. 

/CO. 
Phthalic  anhydride,  C6H4 ,  ^  O,  heated  with  phenol  and 

sulphuric  acid  will  give  phenolphthalein,  a  valuable  and  familiar 

indicator  in  volumetric  analysis. 

/HSO3    .  ,     ,  .  M- 

Sulphanilic  Acid,  CeKi  ^  ,  is  made  by  treating  anihne 

NH2 

with  concentrated  sulphuric  acid.  It  is  a  strong  acid,  occurring 
as  white  crystals,  is  soluble  in  water,  and  is  used  in  the  manu- 
facture of  aniline  dyes  and  also  with  naphthylamine  as  a  reagent 
for  the  detection  of  nitrites. 

Phenyl  Sulphuric  Acid,  C6H5HSO4,  occurs  only  in  combina- 
tion, the  acid  being  unstable  if  attempt  is  made  to  isolate  it. 
Its  potassium  salt  is  present  in  the  urine  as  a  product  of  in- 
testinal putrefaction. 

Phenyl-sulphonic  Acid  may  be  made  by  action  of  oxygen  upon 
the  sulph-hydrate,  similar  to  the  process  described  on  page  232. 

CeHsSH  +  30  =  C6H5SO2HO. 
The  potassium  salt  of  this  acid  heated  with  potassium  hydroxide 
is  a  commercial  source  of  phenol. 

C6H5.SO3K  +  KOH  =  CeHs.OH  -}-  K2SO3. 

Phenol-sulphonic    Acid.  —  When    phenol    is    treated    with 
several  times  its  volume  of  cold,  strong  sulphuric  acid,  phenol 
OH  OH 

sulphonic  acid,  I       |  HSO3  or  |       |,  results.     If  the  mixture  is 


HSO3 


CLOSED-CHAIN  HYDROCARBONS  253 

heated  for  some  time  over  a  water-bath,  the  disulphonic  add 

results.  This  acid,  warmed  with  a  nitrate  and  the  mixture 
treated  with  excess  of  ammonia,  fields  ammonium  picrate,  and 
constitutes  a  dehcate  test  for  nitrates  present  in  drinking  water. 
Phenol-sulphonic  acid  has  been  used  in  dentistry  as  a  thera- 
peutic agent  (as  antiseptic  and  otherwise).  Such  use  is  discussed 
in  detail  by  Herman  Prinz,  M.D.,  D.D.S.,  in  the  Dental  Cosmos 
for  April,  191 2,  with  the  conclusion  that  the  ortho  compound  is 
several  times  more  active  than  either  the  meta  or  para  com- 
pounds; that  a  one  per  cent  solution  is  about  equal  in  antiseptic 
strength  to  a  one  per  cent  phenol  solution,  but  in  this  strength  it 
decalcifies  the  tooth  structure,  discolors  the  teeth,  and  should 
not  be  used  in  the  mouth  on  account  of  its  pronounced  acid 
character. 

H 


Indol,    CsHtN,        I  II  II     ,  is  produced   from   pro- 


//C 

\ 

HC 

c- 

-CH 

1 

II 

II 

HC 

c 

CH 

^C 

/  \ 

N 

/ 

H 

H 

tein  by  the  putrefaction  occurring  in  the  small  intestine,  also  by 
action  of  the  proteolytic  enzyme  of  the  pancreatic  juice  (trypsin). 
The  indol,  by  oxidation  (after  absorption  from  the  intestines), 
becomes  indox}'l,  CsHeNO,  which,  with  potassium  sulphate,  forms 
indoxyl-potassium  sulphate,  CsH6NKS04,  and,  as  such,  is  elimi- 
nated (in  part)  by  the  kidneys.  This  substance  is  a  t>pe  of  the 
so-called  ethereal  or  conjugate  sulphates,  skatoxyl-potassium 
sulphate  (skatol)  and  phenol-potassium  sulphate  being  other 
compoimds  of  this  class.  The  ethereal  sulphates  are  not  precipi- 
tated by  barium  chloride  in  alkahne  solutions,  but  may  be  de- 
composed by  prolonged  boiling  with  hydrochloric  acid  and  then 
precipitated  as  usual. 


254  ORGANIC  CHEMISTRY 

The  oxidation  of  indoxyl  produces  indigo  blue,  and  this  fact 

is  utilized  in  the  qualitative  test  for  indoxyl  in  urine  (q.  v.). 

/  C.CH3,x 
Skatol,  methylindol,    Celit  \  /  CH,  occurs  in    similar 

\nh/ 

manner  to  indoxyl,  and  likewise  passes  into  the  urine  as  an 
ethereal  sulphate  (skatoxyl-potassium  sulphate).  Skatol  is  a 
constituent  of  the  feces  and  possesses  a  strong  fecal  odor. 

Heterocyclic  Compounds.  — •  The  closed-chain  or  cyclic  com- 
pounds are  known  as  isocyclic  or  homocyclic  when  the  atoms 
constituting  the  "ring"  or  nucleus  of  the  molecule  are  all  of 
the  same  sort  (carbocyclic,  if  all  of  carbon),  as  has  been  the  case 
in  all  the  aromatic  compounds  which  we  have  thus  far  taken 
up,  i.e.,  the  structure  of  compounds  has  been  based  upon  the  six- 
carbon  or  benzene  ring.  If  the  ring  is  made  up  of  atoms  of 
different  sorts  the  compound  is  heterocyclic,  and  one  or  two  of 
these  are  of  importance. 

First,  pyridin,  C5H5N,  which  may  be  regarded  as  benzene,  in 
which  one  CH  group  has  been  replaced  by  an  atom  of  nitrogen: 

H 

r 
^^\ 

HC       CH 

I        II 
HC       CH 

It  is  a  liquid  miscible  with  water,  boiling-point  115°  C. 
Second,  quinalin,  C9H7N,  a  colorless  liquid. 

H       H 
C        C 

HC       C       CH 

I         I         II 
HC       C       CH 

^C/^N-" 
H 


CLOSED-CIIA I  .V   //  YCRi  )C.  1 RBONS  255 

Upon  one  or  the  other  of  these  two  bases  may  be  constructed 
the  graphic  formula  of  many  of  the  vegetable  alkaloids. 

A  certain  number  of  alkaloids,  such  as  caffcin  and  thcin  (tri- 
methylxanthin),  are  referable  to  the  purin  nucleus  (page  240). 


PART   VI. 

PHYSIOLOGICAL   CHEMISTRY. 

CHAPTER  XXIX. 

FERMENTS   OR   ENZYMES. 

Physiological  chemistry  treats  of  the  substances  which  go 
to  make  up  the  animal  body,  the  changes  which  these  substances 
undergo  in  the  process  of  digestion  assimilation,  and  the  final 
products  of  metabolism. 

This  subject,  like  others,  will  receive  our  attention  in  out- 
line, with  a  view  simply  to  enable  the  student  to  understand 
the  conditions  which  at  present  seem  to  have  the  most  direct 
bearing  on  dental  science.  The  changes  produced  by  the  class 
of  bodies  known  as  ferments  are  of  great  importance  and  the 
first  to  be  considered. 

If  yeast  is  allowed  to  grow  in  a  sugar  solution  of  moderate 
strength,  the  sugar  molecule  is  split  into  carbonic-acid  gas  and 
alcohol.  The  process  is  one  of  fermentation;  the  yeast  is  the 
ferment.  There  are  various  substances  which  cause  similar 
splitting  of  complex  molecules  into  simpler  compounds.* 

The  distinction  between  the  organized  and  the  unorganized 
ferments  is  no  longer  recognized,  as  it  has  been  proved  that  the 
activity  of  an  organized  ferment  is  due  to  the  presence  of  the 
unorganized  ferment  or  enzyme,  and  we  shall,  by  preference, 
refer  to  these  substances  as  enzymes. 

The  enzymes,  as  a  class,  possess  certain  general  properties 
which  should  be  remembered. 

*  Occasionally  fermentation  may  produce  a  synthesis  (putting  together)  rather 
than  an  analysis  (pulling  apart). 

256 


FERMENTS  OR  ENZYMES  257 

First.  Their  action  is  limited  to  a  very  few  substances; 
i.e.,  the  enzyme  from  yeast,  referred  to  above,  will  convert  a 
few  sugars  only  as  indicated.  They  will  not  act  in  any  other 
way  nor  upon  other  substances. 

Second.  The  enzymes  act  only  at  ordinary  temperatures, 
usually  showing  the  greatest  activity  at  about  the  temperature 
of  the  animal  body,  37°  to  40°  C. 

Third.  Enzymes  act  only  within  very  narrow  limits  as  re- 
gards the  chemical  reaction  (acid  or  alkaline)  of  the  media. 

Fourth.  Enzymes  are  destroyed  (killed)  by  the  heat  of  boil- 
ing water. 

Fifth.  In  regard  to  the  nature  of  their  composition,  many  of 
the  enzymes  are  closely  allied  to  the  proteins. 

An  enzyme  may  be  classified  according  to  the  sort  of  work 
it  does.  Many  of  the  chemical  changes  involved  in  the  utihza- 
tion  of  food  consist  of  breaking  up  a  complex  molecule  and  by 
the  use  of  a  molecule  of  water  forming  new  and  simpler  com- 
pounds. This  sort  of  change  is  called  "Hydrolysis"  and  an 
enzyme  which  will  produce  it  is  a  hydrolytic  enzyme.  By 
hydrolysis  or  hydrolytic  cleavage,  the  molecule  of  cane-sugar, 
C12H22O11,  becomes  two  molecules  of  a  simpler  sugar,  such  as 
glucose,  C6H12O6.      Ci2H220n  4-  H2O  =  2  CeHiaOe. 

Hydrolysis  is  not  dependent  upon  enzyme  action,  as  the 
same  change  is  produced  by  prolonged  boiling  with  very  dilute 
mineral  acids. 

Besides  the  classification  of  enzymes  by  the  character  of  the 
work  they  do,  the  name  of  the  substance  acted  upon  may  also 
be  used  to  designate  an  enzyme;  thus,  a  proteolytic  enzyme 
produces  a  cleavage  of  protein  substances.  A  lipolytic  enzyme 
(lipase)  splits  the  fat  molecule,  etc. 

Several  of  the  digestive  enzymes,  notably  the  proteolytic  or 
flesh-digesting  enz3anes,  such  as  pepsin,  trypsin,  etc.,  exist  in 
the  animal  cell,  not  as  active  agents,  but  as  inactive  parent 
enzymes  which  are  called  pro-enzymes  or  zymogens.     Enzymes 


258  PHYSIOLOGICAL   CHEMISTRY 

of  this  class  are  set  to  work  (liberated  from  the  parent  sub- 
stance) by  a  class  of  substances  known  as  "activators"  (illus- 
trated by  the  enterokinase  of  the  intestine,  page  324). 

Neither  the  zymogen  nor  the  activator  has  of  itself  any  diges- 
tive action  whatever;  a  provision  which  results  in  the  preven- 
tion of  autodigestion  (autolysis)  of  the  cells  containing  them. 

Another  large  and  very  important  class  of  enzymes  are  those 
which  produce  oxidative  changes.  They  may  be  divided  into 
the  oxidases,  which  produce  direct  oxidation,  and  the  peroxidases, 
which  produce  oxidation  only  in  the  presence  or  by  the  aid  of 
peroxide. 

Catalase  is  a  term  which  has  been  applied  to  enzymes,  similar 
in  action  to  the  peroxidases;  i.e.,  they  destroy  a  peroxide  with 
the  formation  of  molecular  oxygen,  although,  according  to 
Hammarsten,  they  differ  from  both  the  oxidases  and  peroxidases 
in  giving  no  reaction  whatever  with  guaiac. 

Oxidases  have  been  found  to  exist  in  saliva,  in  milk,  blood, 
nasal  mucus,  tears,  and  semen,  in  many  of  the  organs,  and  also 
in  the  muscular  tissue.  They  exist  moreover  in  the  vegetable 
kingdom  from  which  the  subject  of  oxidizing  enzymes  was  first 
studied  by  Bertrand  and  Bourquelot.*  The  urine,  bile,  and  in- 
testinal secretions  are  said  not  to  contain  a  ferment  of  this  kind. 

The  name  of  a  specific  enzyme  usually  ends  in  "-ase"  as 
zymase,  the  enzyme  contained  in  yeast;  lipase,  a  fat-splitting 
enzyme;  urease,  the  urine  ferment. 

*  "Enzymes  and  their  Applications,"  Effrant:  Prescott's  translation.  This 
work  is  also  authority  for  statement  immediately  preceding  regarding  the  source 
of  oxidizing  enzjTnes. 


CHAPTER  XXX. 


CARBOHYDRATES. 


Classification:     [Arabinose    )     t. 

,^  ,  ]■     rentoses. 

Xylose  ) 


Sugars 


Dextrose 
Levulose 
Galactose 


Monosaccharides  or  monoses. 


Saccharose 

Maltose       j     Disaccharides  or  dioses. 
.Lactose        J 

Starch    {^t'lrch         ^ 

I  Glycogen 

■     Polysaccharides  or  polyoses. 

Gum        (t^        . 
^  n  1         i  Dextrin 
Cellulose    (  J 

Characteristics.  — •  The  monosaccharides  are  reducing"  bodies 
of  either  the  aldehyde  or  the  ketone  type.  The  termination 
"ose"  is  apphed  to  all  sugars,  and  may  also  be  used  in  designating 
the  type;  thus  dextrose  is  an  "aldose,"  while  levulose  is  a 
"ketose;"  i.e.,  dextrose  is  an  aldehyde,  containing  the  char- 
acteristic —  CHO  group,  while  levulose  is  a  ketone  containing 
the  —  C  =  O  group. 

The  pentoses  (C5H10O5)  are  represented  by  two  important 
compounds,  arabindse  and  xylose.  The  first  of  these  occurs 
occasionally  in  the  urine  (pentosuria),  and  can  be  prepared  by 
boiHng  gum  arable  with  dilute  mineral  acids.  The  second, 
xylose,  has  been  obtained  from  the  pancreas,  but  may  be  pre- 

259 


26o  PHYSIOLOGICAL  CHEMISTRY 

pared  more  easily  from  bran  or  straw  by  boiling  with  dilute 
hydrochloric  acid  (Exp.  162,  page  400). 

The  pentoses,  as  a  class,  boiled  with  dilute  mineral  acid 
(hydrochloric  or  sulphuric),  yield  furfuraldehyde  by  spHtting  off 
the  elements  of  three  molecules  of  water: 

CsHioOs  -  3  H2O  =  C5H4O2. 

The  formation  of  furfuraldehyde  can  be  easily  demonstrated 
by  various  color  reactions  as  given  in  experiment  162,  page  400. 

The  hexoses,  C6H12O6,  also  called  monoses,  occur  quite  gen- 
erally in  nature  (not  true  of  the  pentoses).  They  constitute  the 
various  fruit  sugars,  and  may  be  obtained  by  hydrolysis  of  the 
dioses  and  polyoses. 

They  all  reduce  Fehling's  copper  solution  (galactose  less 
easily  than  the  others),  and  they  are  all  fermented  by  yeast 
(galactose  more  slowly  than  the  others). 

Dextrose  or  Glucose,  CoHioOe,  also  known  as  grape-sugar 
and  as  diabetic  sugar,  occurs  in  grapes,  honey,  etc.  It  is  formed 
by  the  action  of  diastatic  ferments  on  the  disaccharides;  also 
from  many  of  the  polysaccharides.  Glucose  thus  occurs  in  the 
processes  of  digestion  and  constitutes  the  sugar  of  diabetic 
urine.  It  may  be  obtained  commercially  as  a  white  solid,  and 
also  as  a  thick,  heavy  syrup,  known  as  confectioners'  glucose. 
The  commercial  glucose  is  prepared  by  the  action  of  dilute  acids 
on  starch,  when  hydrolysis  takes  place,  as  follows: 

CeHioOs  +  H2O  =  C6H12O6. 

Dextrose  can  be  oxidized  first  to  gluconic  acid  (CH2OH.- 
(CH0H)4.C00H),  and  by  further  oxidation  to  diabasic  sac- 
charic acid: 

C00H.(CH0H)4.C00H. 

This  oxidation  can  be  effected  by  the  use  of  nitric  acid.     Sac- 
charic acid  forms  a  definite  soluble  salt  with  calcium.     Whether 


CA  RBOII YDRA  TES  2  6 1 

the  fact  has  any  bearing  whatever  on  the  relation  of  poor  teeth 
and  excessive  use  of  candy  has  not  been  demonstrated. 

Tests.  —  Glucose  boiled  with  Fehling's  solution  precipitates 
the  red  suboxide  of  copper  (CujO). 

Glucose  responds  to  Molisch's  test  for  carbohydrates,  which 
is  made  with  an  alcoholic  solution  of  a;-naphthol  and  concen- 
trated sulphuric  acid  (Exp.  164).  The  monosaccharides,  of 
which  glucose  is  a  convenient  representative,  may  be  distin- 
guished from  the  other  carbohydrates  by  heating  with  Barfoed's 
solution  (copper  acetate  in  dilute  acetic  acid),  which  is  reduced 
with  precipitation  of  cuprous  oxide. 

Heated  with  phenylhydrazine  solution  nearly  to  the  boiling- 
point  of  water,  glucose  forms  phenylglucosazone,  which  crystal- 
Hzes,  as  the  mixture  cools,  in  characteristic  yellow  needles 
usually  arranged  in  bundles  or  sheaves.     (Plate  VI,  Fig.  i.) 

Osazones  are  the  various  compounds  formed  by  the  different 
sugars  and  phenylhydrazine  when  treated  as  above.  They 
crystallize  in  fairly  distinctive  forms  and  furnish  valuable  tests 
for  the  sugars.  The  phenylhydrazine  test  is  considered  at  least 
ten  times  more  delicate  than  Fehhng's  test.  Glucose  readily 
undergoes  alcoholic  fermentation,  jdelding  C2H5OH  and  CO2. 
(See  Exp.  172,  page  401.) 

Levulose,  C6H12O6,  or  fruit-sugar,  turns  the  ray  of  polarized 
light  to  the  left,  and  to  a  greater  degree  than  glucose  turns  it  to 
the  right.  It  occurs  in  honey  and  in  many  fruits,  and  is  pro- 
duced with  glucose  by  hydrolysis  of  cane-sugar.  Levulose 
forms  an  osazone  not  to  be  distinguished  from  glucosazone.  It 
reduces  copper  solutions  in  a  manner  similar  to  glucose,  and,  like 
it,  is  easily  fermented  by  yeast. 

Galactose  is  the  product  of  the  hydrolysis  of  lactose,  or  milk- 
sugar,  and  some  other  carbohydrates.  It  is  a  crystalhne  sub- 
stance which  reduces  Fehling's  solution  and  ferments  slowly 
with  yeast; 


262  PHYSIOLOGICAL  CHEMISTRY 

DiSACCHARIDES   OR  DiOSES. 

Disaccharides  have  the  general  formula  Ci2H220n.  They  are 
converted  into  the  monosaccharides  by  hydrolysis  brought  about 
either  by  action  of  enzymes  or  by  boiling  with  mineral  acid. 

Cane-sugar,  C12H22O11,  sucrose  or  saccharose,  obtained  from 
the  sugar-cane  (various  varieties  of  sorghum),  also  from  the 
sugar-beet  {Beta  vulgaris)  and  the  sugar-maple  {Acer  saccha- 
rinum).  Cane-sugar  is  a  white  crystalHne  soKd  soluble  in  about 
1/2  part  of  water  and  in  175  parts  of  alcohol  (U.  S.  P.)-  It  does 
not  reduce  copper  solutions,  nor  does  it  form  an  osazone  with 
phenylhydrazine ;  but  it  is  easily  hydrolyzed  with  the  formation 
of  dextrose  and  levulose,  and  then,  of  course,  the  reactions 
peculiar  to  these  substances  may  be  obtained.  It  does  not  fer- 
ment directly,  but,  by  the  action  of  invertin  contained  in  yeast, 
it  takes  up  water,  becoming  glucose  and  levulose  as  above,  these 
latter  sugars  being  easily  fermentable. 

Maltose,  Ci2H220n,  or  malt-sugar,  is  an  intermediate  prod- 
uct in  the  hydrolysis  of  starch,  and  by  further  hydration  be- 
comes two  molecules  of  dextrose:  C12H22O11  -f  H2O  =  2  C6H12O6. 
It  is  formed  in  the  fermentation  of  barley  by  diastase  (the  fer- 
ment of  malt),  and  with  phenylhydrazine  it  produces  an  osazone 
distinguished  from  glucosazone  and  lactosazone  by  its  micro- 
scopical appearance  (Plate  VI,  Fig.  2)  and  its  melting-point. 

Lactose,  C12H22O11,  obtained  from  milk,  is  a  disaccharide 
with  far  less  sweetening  power  than  sucrose.  It  forms  an 
osazone  which  crystalHzes  in  small  burr-shaped  forms  (Plate  VI, 
Fig.  3).  It  reduces  Fehling's  solution,  but  does  not  reduce 
Barfoed's  solution.  It  resists  fermentation  in  a  marked  degree. 
Upon  hydration  it  is  converted  into  dextrose  and  galactose. 

PoLYOSES  —  Polysaccharides. 

Starch.  —  This  well-known  and  widely  distributed  plant-con- 
stituent is  a  carbohydrate  represented  by  CeHioOs,  the  actual 
molecule,  however,  being  many  times  this  simple  formula.     The 


PLATE   VI.  —  PHYSIOLOGICAL   CHEMISTRY 


Fig.  I. 
Glucosazone. 


Fig.  3. 
Lactosazone. 


Fig.  2. 
Maltosazone. 


Fig.  4. 
Wheat  Starch. 


Fig.  5. 
A,  Corn  starch;  B,  Rice  starch. 


FiG.  6. 
A,  Potato  starch;  B,  Arrowroot  starch. 


CARBOIIYDRA  TES  263 

microscopical  appearance  of  the  starch  granule  is  quite  charac- 
teristic, and  recognition  of  the  more  common  starches  by  this 
method  is  not  at  all  ditlicult  (see  Plate  VI,  page  262). 

Starch  is  not  soluble  in  cold  water,  but  in  hot  water,  or  in 
solutions  containing  "amylolytic"  enzymes,  or  in  solutions 
containing  certain  chemical  substances,  as  chloride  of  zinc  or  of 
magnesium,  dilute  hydrochloric  or  sulphuric  acid,  capable  of 
forming  hydrolytic  products,  the  starch  granules  swell  up,  and 
ultimately  dissolve,  being  converted  into  dextrose.  The  con- 
version, however,  takes  place  in  several  well-defined  steps,  as 
follows:  Soluble  starch  is  first  formed,  answering  the  same  chem- 
ical test  with  iodine  (Exp.  245,  page  416);  next,  erythrodextrin, 
which  gives  a  red  color  with  iodine  solution;  then  achroo-  and 
maUodexirin,  which  give  no  color  with  iodine,  but  react  slightly 
with  Fehhng's  copper  solution;  then  maltose,  also  negative  with 
iodine,  but  reacting  strongly  with  Fehling's  solution;  and  finally 
dextrose. 

Dextrin  (CeHioOs)  is  a  yellowish  powder,  also  known  as 
British  gum;  is  formed  from  starch,  as  indicated  above;  con- 
stitutes to  a  considerable  extent  the  "crust"  of  bread;  is  solu- 
ble in  water,  the  solution  giving  a  red  color  with  iodine,  and  is 
also  distinguished  from  starch  by  its  failure  to  give  a  precipitate 
with  solution  of  tannic  acid. 

Glycogen,  or  animal  starch,  is  a  carbohydrate,  with  the  gen- 
eral formula  CeHioOs,  occurring  principally  in  the  liver,  and  to 
a  lesser  extent  in  nearly  all  parts  of  the  animal  body.  Freslily 
opened  oysters  are  a  convenient  source  of  the  substance  for 
laboratory  demonstration.  It  occurs  in  horse-flesh  in  consider- 
ably larger  proportions  than  in  human  flesh. 

Properties.  —  Glycogen  is  a  white  powder  without  odor  or 

taste.     It  dissolves  in  water,  producing  an  opalescent  solution. 

It  is  closely  allied  to  the  starches  of  vegetable  origin  in  that  the 

products  of  its  hydrolysis  are  dextrin  *  and  ultimately  dextrose. 

*  Foster's  Text-book  of  Physiology. 


264  PHYSIOLOGICAL  CHEMISTRY 

It  differs  in  its  ready  solubility  in  water,  and  in  the  fact  that 
it  is  precipitated  by  66%  alcohol,  also  in  its  power  of  rotation, 
which  is  much  stronger  than  that  of  starch. 

Physiology.  —  Glycogen  is  formed  by  the  liver,  and  stored  by 
this  same  organ  for  future  use.  It  is  derived  principally  from 
carbohydrates,  but  may  also  be  derived  from  proteins.  It  dis- 
appears during  starvation.  In  dead  liver  or  muscle  it  rapidly 
undergoes  hydrolytic  change  with  the  production  of  a  reducing 
sugar. 

Cellulose,  CeHioOs,  is  a  carbohydrate  which  occurs  as  a 
principal  constituent  of  woody  liber,  and  which  may  be  found 
in  the  laboratory  in  nearly  a  pure  state,  as  absorbent  cotton 
or  Swedish  filter-paper.  It  is  insoluble  in  water,  alcohol,  or 
dilute  acids;  it  may  be  dissolved,  however,  by  an  ammoniacal 
copper  solution.  It  is  converted  into  monosaccharides  by  acids, 
only  after  first  treating  with  concentrated  sulphuric  acid,  which 
partially  dissolves  it.  Cellulose  aids  digestion  in  a  purely  me- 
chanical way  by  separating  the  digestible  matter  and  allowing 
easier  access  of  digestive  ferments.  The  celluloses  may  be 
divided  into  three  classes:  those  resisting  hydrolysis  and  con- 
sequently lacking  nutritive  value,  such  as  flax,  cotton  fibers, 
and  hemp;  those  which  hydrolyze  slightly,  which  include  the 
ligno-celluloses  and  may  be  utilized  as  food  by  herbiverous 
animals;  the  pseudo-celluloses,  which  are  hydrolysed  quite 
easily  and  may  be  digested  by  enzymes. 

When  cellulose  is  treated  with  a  mixture  of  nitric  and  sulphuric 
acids,  it  is  converted  into  nitro-substitution  products  which  are 
known  as  guncotton.  The  soluble  cotton  from  which  collodion 
is  prepared,  by  solution  in  a  mixture  of  ether  and  alcohol,  is  a 
mixture  of  tetra-  and  pentanitrates,  while  the  more  explosive 
but  insoluble  guncotton  is  a  hexanitrate,  formerly  known  as 
trinitrocellulose. 


CHAPTER  XXXI. 
FATS   AND   OILS. 

Natural  fats  and  oils  of  animal  or  vegetable  origin  are 
mixtures  of  several  compound  glyceryl  ethers  or  esters  (see  page 
215),  and  by  subjecting  them  to  cold  and  pressure  they  may 
be  separated  into  two  portions,  one  solid  with  comparatively 
high  melting-point,  and  the  other  liquid  at  ordinary  tempera- 
tures. The  solid  portion  is  known  as  the  stearopten,  and  the 
liquid  as  the  eleopten,  of  the  fat.  Thus  from  beef-fat,  we  may 
express  a  fluid  eleopten  consisting  largely  of  olein  and  obtain 
as  a  residue  a  stearopten,  stearin.  The  stearopten  of  the  vol- 
atile or  essential  oils  are  classed  as  camphors,  on  account  of 
their  resemblance  to  ordinary  camphor.  Menthol,  from  oil  of 
peppermint,  and  th3rmol,  from  oil  of  thyme,  are  examples  of  this 
class  of  compounds,  both  of  which  are  largely  used  in  dental 
practice. 

Properties.  —  Fats  are  insoluble  in  water,  easily  dissolved  by 
ether,  chloroform,  and  carbon  disulphide,  less  easily  by  alcohol, 
crystallizing  on  evaporation  of  the  solvent.  (Plate  VII,  Fig.  3, 
page  287.)  They  are  emulsified  by  mechanical  subdivision  of 
the  fat  globules,  in  the  presence  of  some  agent  which  prevents 
their  reuniting.  The  vegetable  mucilages,  soap,  jelly,  etc.,  are 
such  emulsifying  agents.  On  exposure  to  the  air,  fats  and  oils 
are  more  or  less  easily  oxidized,  which  causes  a  separation  of  the 
fat  acid.  This  produces  an  unpleasant  odor  or  taste,  and  the 
fat  is  said  to  become  rancid.  - 

Chemistry.  —  The  principal  organic  acids  entering  into  the 
composition  of  fat  are  Stearic  acid,  HC18H35O2,  solid,  white, 

without  odor  or  taste,  melts  at  70°  C;  Palmitic  acid,  HC16H31O2, 

265 


266  PHYSIOLOGICAL  CHEMISTRY 

resembles  stearic  acid  in  its  physical  properties  but  melts  at 
62°  C;  Oleic  acid,  HCisHs  O2,  contains  two  CH=  groups  with 
double-bonded  carbons  in  the  middle  of  the  chain.  This  last 
acid  is  fluid  at  ordinary  temperatures  and  predominates  in  the 
softer  animal  fat.  Its  glyceryl  ester,  olein,  constitutes  seventy 
to  eighty-five  per  cent,  of  human  fat  (percentage  said  to  increase 
with  age)  and  thirty-six  per  cent,  of  butter. 

Physiology.  —  Fats  are  not  digested  to  any  appreciable  ex- 
tent until  they  reach  the  intestine;  here  they  are  broken  up 
by  a  fat-splitting  enzyme,  emulsified,  and  to  a  slight  extent 
saponified,  after  which  they  may  be  absorbed  by  the  system 
(see  Pancreatic  Digest  on). 

Glyceryl  Palmitate,  C3H5(Ci6H3i02)3,  tripalmitin;  glyceryl 
stearate,  C3H5(Ci8H3502)3,  tristearin,  and  glyceryl  oleate, 
C3H5(Ci8H3302)3,  trlolcin ;  these  in  varying  proportions  make  up 
the  greater  part  of  animal  and  vegetable  fats  and  oils. 

The  prefix  "tri"  is  used  because  the  "mono"  and  "di" 
compounds,  as  monopalmitin,  C3H5(OH)2  — C16H31O2,  etc.,  are 
possible  and  may  be  prepared  by  synthesis.  Triolein  is  liquid 
at  ordinary  temperature,  solidifies  at  —  6°  C,  is  a  "double- 
bonded"  compound,  hence  forms  addition-products  with  the 
halogens  as  stearin  and  palmitin  cannot  do,  since  they  are 
"saturated  hydrocarbons." 

The  amount  of  chlorine  or  bromine  which  a  fat  or  oil  can  thus 
absorb  is  an  index  of  the  proportion  of  unsaturated  fatty  acids 
contained  in  it,  and  hence  becomes  a  valuable  method  of  identi- 
fication.    Ohve-oil  and  lard-oil  contain  large  amounts  of  olein. 

Tripalmitin  melts  at  66°  C,  is  usually  obtained  from  palm- 
oil.  Tristearin  melts  at  72°  C,  occurs  with  palmitin  and  olein 
in  beef-fat,  mutton-tallow,  etc.,  the- consistence  of  the  fat  being 
dependent  upon  the  proportions  of  the  constituent  esters. 

The  fats,  stearin  for  example,  may  be  spht  into  glycerol  and 
fatty  acid  by  steam  under  pressure  as  follows: 

C3H5(Cl8H3502)3  +  3  H2O    =    C3H5(OH)3   +  3  HC18H35O2. 


FATS  AND  OILS  367 

A  partial  result  of  this  sort  is  brought  about  by  the  fat-splitting 
enzyme  (lipase)  of  the  pancreatic  juice  (see  Steapsin). 

Saponification  of  the  fats  by  caustic  alkaU  takes  place  as 
follows : 

C3H5(Cl8H350o)3   +  3  KOH    =   C3H5(OH)3  +  3  KCl,H3502. 

The  potassium  salts  of  the  fatty  acids  constitute  the  soft 
soaps,  while  the  sodium  salts  are  in  general  the  hard  soaps. 
The  "salting-out"  process  in  soap  manufacture  brings  about  a 
double  decomposition  resulting  in  the  production  of  ordinary  soap. 

Volatile  Oils  do  not  contain  the  glyceryl  base  but  rather  a 
group  of  hydrocarbons  known  as  the  "  terpenes."  The  formula 
is  (C5H8)2,  the  most  important  of  the  group  is  CioHie  from  oil  of 
turpentine  and  many  of  the  essential  oils. 

The  odor  of  the  volatile  oils  seems  to  be  dependent  upon  the 
presence  of  water  and  air;  for  example,  oil  of  clove  distilled  over 
lime  and  in  atmosphere  free  from  oxygen  has  little  odor.  The 
presence  of  oxygen  and  moisture  restores  the  characteristic  odor. 

Lecithin  has  been  classified  as  a  phosphorized  fat;  it  occurs 
in  nervous  tissue,  in  the  bile,  and  is  obtained  in  considerable 
quantity  from  the  yolk  of  eggs.  It  contains  two  fat  acid  radicals 
combined  with  glycerol,  phosphoric  acid  and  choline.  Lecithin 
is  soluble  in  chloroform,  alcohol,  ether  and  benzene,  and  may  be 
obtained  in  crystalline  form  from  the  alcoholic  solution.  -  The 
fatty  acid  radicals  are  not  always  the  same  or  necessarily  alike. 
Lecithin  may  be  represented  by  the  following  formula: 

CH2  —  C17H35CO2 
I 

CH  —  C17H33CO2 
I 

CHoO 
I 
0  =  P  -OH.O 
I 

C2H4 
I 
(CH3)3N-OH 


268  PHYSIOLOGICAL   CHEMISTRY 

and  its  decomposition  by  the  following  reaction: 

C44H90NPO9  +  3  H2O  =  2  Ci8H3«02  +  C3H9PO6  +  CsHisNOa 

Lecithin  Stearic        Glycero-        Choline 

acid  phosphoric 

acid 


CHAPTER  XXXII. 
PROTEINS. 

Protein  *  is  a  general  term  used  to  designate  the  nitrogenized 
bodies  which  constitute  the  greater  proportion  of  animal  tissue. 

While  meat  and  "protein"  are  usually  associated,  it  must 
not  be  forgotten  that  meat  is  not  the  exclusive  source  of  protein, 
for  we  usually  find  protein  in  vegetable  substances  and  often  to 
a  considerable  extent. 

Unlike  the  other  two  great  divisions  of  food  substances  (carbo- 
hydrates and  fats),  the  structure  of  the  protein  molecule  is  so 
complex  that  with  a  few  exceptions  of  the  simplest  kind  its 
representation  has  not  been  attempted. 

The  protein  molecule  contains  nitrogen  (often  as  the  amino 
group  NH2)  in  addition  to  the  carbon,  hydrogen,  and  oxygen  of 
the  carbohydrates  and  fats.  It  frequently  contains  sulphur, 
often  phosphorus,  and  occasionally  the  metallic  elements,  par- 
ticularly iron. 

As  examples  of  the  complexity  of  protein  molecules,  the 
following  proposed  formulae  are  given  in  Hawk's  Physiological 
Chemistry. 

Serum  albumin,  C450H720N116S6O140. 

Oxyhemoglobin,  C658Hii8iN207S2Fe02io. 

While  a  classification  of  proteins  according  to  their  chemical 
composition  is  at  present  practically  impossible,  the  following 
may  be  of  interest. 

After  Hofmeister,  Ergebnisse  der  Physiologie,  Jahrg.  I. 

*  The  term  proteid  was  formerly  used  instead  of  protein,  but  in  accordance 
with  the  recommendations  of  the  Committees  of  the  American  Physiological  and 
Biochemical  Societies,  it  has  been  abandoned.  The  classification  and  definitions 
herewith  given  are  taken  from  their  recommendation  as  printed  in  Science,  Vol. 
27,  No.  692,  page  554. 

269 


270  PHYSIOLOGICAL  CHEMISTRY 

I.   Groups  of  the  Aliphatic  Series. 

A.  Group  containing  C,  N,  H. 

The  only  representative  known  is  the  guanidine  radical 
(CNH).NH2. 

B.  Groups  containing  C,  N,  H,  O. 

1.  Amino-acids. 

(a)    Monamino-acids. 

1.  Monobasic  monamino-acids,  C„H2„+iN02. 

C2  is  glycocoU. 

C3  is  alanin. 

C5  is  amino  valerianic  acid. 

Ce  is  leucine,  which  occurs  universally. 

2.  Dibasic  monamino-acids,  C„H2„_iN04. 

C4  is  asparaginic  acid. 
Co  is  glutaminic  acid. 
{h)    Diamino-acids  (all  monobasic  acids). 
C2  is  diaminoacetic  acid  (rare). 
Argynine  (guanidine-a-aminovalerianic  acid).     Here  the 
diamino-acid  is  combined  with  the  guanidine  radical, 

NH2.NH.C.NH.CH2.(CH2)2.CH.NH2COOH. 

Lysine  (a-e-diaminocapronic  acid), 

NH2.CH2.(CH2)3.CH.NH2.COOH. 

2.  Amino-alcohols. 

Glucosamine,  C6Hii05(NH2),  a  hexose  into  which 
NH2  has  entered  the  carbohydrate  group  of  the 
protein  molecule. 

C.    Groups  containing  C,  N,  H,  O,  S. 

Cystein,     aminothiolactic     acid,    CH2.SH.CH(NH2).- 

COOH. 
Cystin,  the  sulphide  of  cystein,  C6H12S2N2O4. 
a-thiolactic  acid. 


PROTEINS  271 

II.   Groups  of  the  Aromatic  Series. 

A.  Phenylalanin,  C6H5.CH2.CH(NH2).COOH. 

B.  Tyrosin,  C6H4.0H.CH2.CH(NH2).COOH. 

III. 
A.   Pyrrol  group. 

I.   a-pyrrolidine  carbonic  acid, 

CH  -  CH  -  CH  -  CH.COOH 

' NH -' 


B.  Indol  group. 

1.  Indol,  see  page  253. 

2.  Skatol  (methyl  indol),  see  page  254. 

3.  Tryptophane  (indolaminopropionicacid), 

CiiHisNsO.. 

4.  Skatosin,  C10H16N2O2. 

C.  Pyridin  group. 

Pyridin,  see  structural  formula  on  page  254. 

D.  Pyrimidin  group. 

Histidin:  structural  formula  probably 

NH CH 

I  II 

CH  =  C--N-CH2-CHNH2-COOH. 

Excepting  the  carbohydrate  group,  and  perhaps  the  pyridin 
and  pyrimidin  groups,  which  are  absent  in  a  few  special  in- 
stances, all  typical  proteins  contain  at  least  one  representative 
from  each  group. 

A  much  more  practical  classification,  based  in  part  upon  the 
properties  of  the  substance,  is  that  suggested  by  the  Joint  Com- 
mittees on  Protein  Nomenclature  (footnote,  page  269). 

"Since  a  chemical  basis  for  the  nomenclature  of  the  proteins 


272  PHYSIOLOGICAL   CHEMISTRY 

is  at  present  not  possible,  it  seems  important  to  recommend 
a  few  changes  in  the  names  and  definitions  of  generally  accepted 
groups,  even  though,  in  many  cases,  these  are  not  wholly  satis- 
factory."    The  recommendations  are  as  follows: 

First.     The  word  proteid  should  be  abandoned. 

Second.  The  word  protein  should  designate  that  group  of 
substances  which  consist,  so  far  as  is  known  at  present,  essen- 
tially of  combinations  of  a-amino  acids  and  their  derivatives, 
e.g.,  a-aminoacetic  acid  or  glycocoll;  a-amino  propionic  acid  or 
alanin;  phenyl-a-amino  propionic  acid  or  phenylalanin ;  guani- 
dine-amino  valerianic  acid  or  arginine,  etc.,  and  are  therefore 
essentially  polypeptides. 

Third.  That  the  following  terms  be  used  to  designate  the 
various  groups  of  proteins: 

I.   Simple  Proteins. 

Protein  substances  which  yield  only  a-amino  acids  or  their 
derivatives  on  hydrolysis. 

Although  no  means  are  at  present  available  whereby  the 
chemical  individuality  of  any  protein  can  be  established,  a 
number  of  simple  proteins  have  been  isolated  from  animal  and 
vegetable  tissues  which  have  been  so  well  characterized  by  con- 
stancy of  ultimate  composition  and  uniformity  of  physical 
properties  that  they  may  be  treated  as  chemical  individuals 
until  further  knowledge  makes  it  possible  to  characterize  them 
more  definitely. 

The  various  groups  of  simple  proteins  may  be  designated  as 
follows : 

(a)  Albumins.  —  Simple  proteins  soluble  in  pure  water  and 
coagulable  by  heat;  e.g.,  ovalbumin,  serum  albumin,  lactalbumin, 
vegetable  albumins. 

(b)  Glflbulins.  —  Simple  proteins  insoluble  in  pure  water,  but 
soluble  in  neutral  solutions  of  salts  of  strong  bases  with  strong 


PROTEINS  273 

acids;*  e.g.,t  serum  globulin,  ovoglobulin,  edestin,  amandin,  and 
other  vegetable  globulins. 

(c)  Glulclins.  —  Simple  proteins  insoluble  in  all  neutral 
solvents  but  readily  soluble  in  very  dilute  acids  and  alkalies ;{ 
e.g.,  glutenin. 

{d)  Alcohol-soluble  Proteins  {Prolamines).  —  Simple  proteins 
soluble  in  relatively  strong  alcohol  (70  to  80  per  cent),  but  in- 
soluble in  water,  absolute  alcohol,  and  other  neutral  solvents  ;§ 
e.g.,  zein,  gliadin,  hordein,  and  bynin. 

{e)  Albuminoids.  —  Simple  proteins  which  possess  essentially 
the  same  chemical  structure  as  the  other  proteins,  but  are 
characterized  by  great  insolubility  in  all  neutral  solvents ;||  e.g., 
elastin,  collagen,  keratin. 

(J)  Histones.  —  Soluble  in  water  and  insoluble  in  very  dilute 
ammonia  and,  in  the  absence  of  ammonium  salts,  insoluble  even 
in  an  excess  of  ammonia;  yield  precipitates  with  solutions  of 
other  proteins  and  a  coagulum  on  heating  which  is  easily  soluble 
in  very  dilute  acids.  On  hydrolysis  they  yield  a  large  number 
of  amino  acids,  among  which  the  basic  ones  predominate;  e.g., 
globin,  thymus  histone,  scombrone. 

{g)  Protamines.  —  Simpler  polypeptides  than  the  proteins  in- 
cluded in  the  preceding  groups.  They  are  soluble  in  water,  un- 
coagulable  by  heat,  have  the  property  of  precipitating  aqueous 
solutions  of  other  proteins,  possess  strong  basic  properties  and 

*  The  precipitation  limits  with  ammonium  sulphate  should  not  be  made  a 
basis  for  distinguishing  the  albumins  from  the  globulins. 

t  The  examples  of  the  various  proteins  are  those  given  by  Prof.  P.  B.  Hawk. 

X  Such  substances  occur  in  abundance  in  the  seeds  of  cereals  and  doubtless 
represent  a  well-defined  natural  group  of  simple  proteins. 

§  The  sub-classes  defined  (a,  h,  c,  d)  are  exemplified  by  proteins  obtained  from 
both  plants  and  animals.-  The  use  of  appropriate  prefixes  will  suffice  to  indicate 
the  origin  of  the  compounds,  e.g.,  ovoglobulin,  myoalbumin,  etc. 

II  These  form  the  principal  organic  constituents  of  the  skeletal  structure  of 
animals  and  also  their  external  covering  and  its  appendages.  This  definition  does 
not  provide  for  gelatin,  which  is,  however,  an  artificial  derivative  of  collagen. 


2  74  PHYSIOLOGICAL  CHEMISTRY 

form  stable  salts  with  strong  mineral  acids.  They  yield  com- 
paratively few  amino  acids,  among  which  the  basic  amino  acids 
greatly  predominate;  e.g.,  salmine,  sturine,  clupeine,  scombrine. 

II.   Conjugated  Proteins. 

Substances  which  contain  the  protein  molecule  united  to 
some  other  molecule  or  molecules  otherwise  than  as  a  salt. 

(a)  Nucleo proteins.  —  Compounds  of  one  or  more  protein 
molecules  with  nucleic  acid;  e.g.,  cystoglobulin,  nucleohistone. 

{h)  Glycoproteins.  —  Compounds  of  the  protein  molecule 
with  a  substance  or  substances  containing  a  carbohydrate  group 
other  than  a  nucleic  acid;  e.g.,  mucins  and  mucoids  (osseomu- 
coid, tendomucoid,  ichthulin,  hehcoprotein) . 

(c)  Phospho proteins.  —  Compounds  of  the  protein  molecule 
with  some,  as  yet  undefined,  phosphorus-containing  substance 
other  than  a  nucleic  acid  or  lecithins;*  e.g.,  caseinogen,  vitellin. 

(d)  Hemoglobins.  —  Compounds  of  the  protein  molecule  with 
hematin  or  some  similar  substance;  e.g.,  hemoglobin,  hemo- 
cyanin. 

(e)  Lecitho proteins.  —  Compounds  of  the  protein  molecule 
with  lecithins  (lecithans,  phosphatides);  e.g.,  lecithans,  phos- 
phatides. 

III.   Derived  Proteins. 

I.  Primary  Protein  Derivatives.  —  Derivatives  of  the  pro- 
tein molecule  apparently  formed  through  hydrolytic  changes 
which  involve  only  slight  alterations  of  the  protein  molecule. 

(a)  Proteans.  —  Insoluble  products  which  apparently  result 
from  the  incipient  action  of  water,  very  dilute  acids  or  enzymes; 
e.g.,  myosan,  edestan. 

{b)    Metaproteins.  —  Products  of  the  further  action  of  acids 

*  The  accumulated  chemical  evidence  distinctly  points  to  the  propriety  of 
classifying  the  phosphoproteins  as  conjugated  compounds;  i.e.,  they  are  possibly 
esters  of  some  phosphoric  acid  or  acids  and  protein. 


PROTEINS  275 

and  alkalies  whereby  the  molecule  is  so  far  altered  as  to  form 
products  soluble  in  very  weak  acids  and  alkalies,  but  insoluble 
in  neutral  fluids. 

This  group  will  thus  include  the  familiar  "acid  proteins"  and 
"alkali  proteins,"  not  the  salts  of  proteins  with  acids;  e.g.,  acid 
metaproteins  (acid  albuminate),  alkali  metaprotein  (alkali 
albuminate). 

(c)  Coagulated  Proteins.  —  Insoluble  products  which  result 
from  (i)  the  action  of  heat  on  their  solutions,  or  (2)  the  action 
of  alcohols  on  the  protein. 

2.  Secondary  Protein  Derivatives j^'  —  Products  of  the  further 
hydrolytic  cleavage  of  the  protein  molecule. 

{a)  Proteoses.  —  Soluble  in  water,  uncoagulated  by  heat,  and 
precipitated  by  saturating  their  solutions  with  ammonium  sul- 
phate or  zinc  sulphate ;t  e.g.,  protoproteose,  deuteroproteose. 

(Jj)  Peptones.  —  Soluble  in  water,  uncoagulated  by  heat,  but 
not  precipitated  by  saturating  their  solutions  with  ammonium 
sulphate ;{   e.g.,  antipeptone,  amphopeptone. 

(c)  Peptides.  -. —  Definitely  characterized  combinations  of  two 
or  more  amino  acids,  the  carboxyl  group  of  one  being  united 
with  the  amino  group  of  the  other,  with  the  elimination  of  a 
molecule  of  water;  §  e.g.,  dipep tides,  tripeptides,  tetrapeptides, 
pentapep  tides. 

Albumins. 

The  albumins  are  conveniently  represented  by  egg-albumin 
and  serum-albumin.     They  are  soluble  in  water,  respond  to  the 

*  The  term  secondary  hydrolytic  derivatives  is  used  because  the  formation  of  the 
primary  derivatives  usually  precedes  the  formation  of  these  secondary  derivatives. 

t  As  thus  defined,  this  term  does  not  strictly  cover  all  the  protein  derivatives 
commonly  called  proteoses;   e.g.,  heteroproteose  and  dj^sproteose. 

X  In  this  group  the  kyrins  may  be  included.  For  the  present  we  believe  that 
it  wall  be  helpful  to  retaiii  this  term  as  defined,  reserving  the  expression  peptide 
for  the  simpler  compounds  of  definite  structure,  such  as  dipeptides,  etc. 

§  The  peptones  are  undoubtedly  peptides  or  mixtures  of  peptides,  the  latter 
being  at  present  used  to  designate  those  of  definite  structure. 


276  PHYSIOLOGICAL  CHEMISTRY 

general  protein  reactions  (Exp.  187,  page  405,  etc.),  and  may  be 
completely  precipitated  by  saturation  of  the  solution  by  am- 
monium sulphate.     Albumin  is  coagulated  by  heat  (75°  to  80°  C). 

Egg-albumin  differs  from  serum-albumin  in  that  it  is  not 
absorbed  when  injected  into  the  circulation,  but  appears  un- 
changed in  the  urine.  Egg-albumin  is  readily  precipitated  from 
aqueous  solution  by  alcohol,  while  serum-albumin  is  precipi- 
tated only  with  difficulty.  Albumins  in  general  form,  with 
acids  or  with  alkalies,  derived  albumins  known  as  acid  or  alkali 
albumins  or  albuminates  (acid  or  alkali  metaproteins) .  An  acid 
albumin  derived  from  myosin  is  known  as  syntonin.  It  differs 
but  slightly  from  other  acid  albumins.  The  acid  and  alkali 
albumins  are  both  precipitated  by  neutralization,  but  neither  of 
them  are  coagulated  by  heat. 

If  the  hydrolysis  of  albumin  is  brought  about  by  hydrochloric 
acid  at  the  body  temperature,  it  causes  the  molecule  to  split  into 
two  proteins,  one  known  as  antialbuminate  and  the  other  as  hemi- 
albumose,  these  in  turn  becoming  respectively  antialbumid  and 
hemipeptone.  Sulphuric  acid  at  a  boiling  temperature  produces 
a  similar  change,  except  that  the  hemipeptone  is  further  changed 
to  leucin  and  tyrosin.  Digestive  ferments,  pepsin,  and  trypsin 
produce  antialbumose,  hemiantipeptone,  and  hemialbumose,  but 
trypsin  alone  converts  the  hemipeptone  into  leucin  and  tyrosin. 

Albumin  normally  occurs  in  all  the  body  fluids  except  in  the 
urine.  The  amount  in  milk  is  extremely  slight;  the  amount  in 
saliva  seems  to  vary  in  inverse  proportion  to  mucin.  Albumin 
occurring  in  urine  in  appreciable  quantity  is  always  abnormal, 
although  in  many  cases  it  has  no  serious  significance  unless 
persistently  present  in  more  than  the  slightest  possible  trace. 

Globulins. 

The  globulins  occur  in  both  plants  and  animals,  and  crushed 
hemp  seed  may  be  used  as  a  convenient  source  for  laboratory 
experiment.     It  is  also  associated  with  albumin  in  blood-plasma, 


PROTEINS 


277 


and  may  be  separated  from  it  by  half  saturation  with  ammonium 
sulphate,  which  precipitates  the  globuhn  only,  but  it  is  not  to 
be  distinguished  by  the  ordinary  protein  tests  and  reactions. 
The  albumin  of  albuminous  urine  always  consists  of  a  mixture 
of  these  two  proteins,  globulin  and  albumin,  not,  however,  al- 
ways in  the  same  proportion.  The  globulins  are  not  soluble  in 
distilled  water  as  the  albumins  are,  but  a  very  small  quantity  of 
neutral  salt,  such  as  sodium  chloride,  will  serve  to  effect  the  solu- 
tion. Globuhn  is  thrown  out  of  solution  by  action  of  carbon 
dioxide  as  a  white  flocculent  precipitate.  By  dialysis  the  in- 
organic salts  necessary  for  its  solution  will  be  removed  and  the 
protein  will  be  precipitated.  It  is  also  thrown  out  by  saturation 
of  sodium  chloride  or  magnesium  sulphate.  Globulin  is  coagu- 
lated by  heat  at  practically  the  same  temperature  as  serum- 
albumin;  i.e.,  75°  C. 

The  glutelins  and  prolamines  thus  far  studied  have  been 
mostly  obtained  from  vegetable  sources. 

Glutenin  constitutes  about  one-half  of  wheat  gluten,  and 
the  prolamines  mentioned  on  page  273;  Zein  is  obtained  from 
maize,  Hordein  from  barley,  Ghadin  from  wheat  or  rye,  and 
Bynin  from  malt. 

Albuminoids. 

Albuminoids  are  the  simple  proteins  characterized  by  pro- 
nounced insolubiHty  in  al  neutral  saUvas,  and  the  common  exam- 
ples are  Keratin,  from  nails  and  hoofs,  etc. ;  Collagen,  from  bone 
and  connective  tissue;  and  Elastin,  from  tendons  and  ligaments. 

The  differences  in  these  substances  are  slight,  the  keratin 
being  less  soluble  and  less  easily  acted  upon  by  digestive  ferments 
than  either  of  the  ""other  two.-  Keratin  also  contains  more  sul- 
phur. It  is  the  principal  constituent  of  horn,  nails,  hair,  feathers, 
egg  membrane,  and  some  shells,  such  as  turtle  and  tortoise. 
The  sulphur  content  of  these  various  sources  differs  considerably. 


278  PHYSIOLOGICAL  CHEMISTRY 

ranging  from  about  5%  in  hair,  about  3%  in  nail  and  horn,  to 
1.4%  in  egg  membrane. 

The  keratins  are  characterized  by  the  fact  that  the  sulphur 
which  they  contain  is  loosely  combined;  i.e.,  easily  separated  by 
the  formation  of  hydrogen  sulphide  and  other  sulphur  com- 
pounds as  proved  by  experiment  No.  207.  The  keratins  are 
insoluble  in  dilute  acids  and  unaffected  by  any  of  the  diges- 
tive ferments;  they  do,  however,  dissolve  in  the  caustic  alkali 
solutions,  and  may  be  used  as  the  source  of  leucin,  tyrosin, 
cystin,  and  other  well-known  products  of  protein  digestion. 

Keratins  heated  with  water,  under  pressure,  to  150°  C.  will 
decompose  with  the  formation  of  mercaptan,  hydrogen  sulphide, 
and  a  substance  resembling  the  proteoses. 

Collagen,  upon  hydrolization  with  boiling  water,  produces 
gelatin,  which  is  a  characteristic  property  of  this  class  of  pro- 
teins. It  may  be  dissolved  by  both  the  gastric  and  pancreatic 
juices,  especially  if  previously  treated  with  warm  acidulated 
water.  Collagen  contains  less  sulphur  than  keratin  and  is  ob- 
tained particularly  from  the  tendo  Achillis  which  contains  about 
32%  of  this  albuminoid  and  63%  of  water.  Collagen  responds 
to  the  general  color  tests  for  the  proteins. 

Elaslin  contains  the  least  sulphur  of  any  of  the  three  sub- 
stances which  we  have  considered.  It  may  be  obtained  from 
the  ligamentum  nuchas  of  an  ox,  which  contains  about  3i|% 
of  elastin  and  58%  of  water,  by  chopping  the  ligament  finely 
and  extracting  for  two  or  three  days  with  //(z//-saturated  solution 
of  calcium  hydroxide.  Like  collagen,  it  is  dissolved  upon 
prolonged  treatment  with  proteolytic  ferments. 

Reticulin  occurs  as  a  fibrous  part  of  lymph  glands.  It  is 
insoluble  in  water  and  is  not  digested  by  pepsin  or  trypsin.  It 
does  not  respond  to  Millon's  test  for  proteins. 


PROTEINS  279 


Bone. 


If  all  organic  matter  is  burned  off  from  bone,  there  remains 
the  bone-earth,  so-called,  made  up  of  the  phosphates  and  car- 
bonates of  lime  and  magnesia,  with  sHght  amounts  of  chlorine, 
fluorine,  and  of  sulphates,  the  proportion  being  practically  the 
same  as  given  for  dentine,  under  Teeth,  on  page  189.  Because 
in  some  diseases,  in  which  the  bones  are  softened  or  decalcified 
(as  osteomalacia),  the  relation  of  the  calcium  oxide  and  phos- 
phorous pentoxide  remains  unchanged,  it  has  been  claimed  that 
these  substances  exist  in  the  bone  in  the  form  of  a  definite 
phosphate-carbonate  containing  three  molecules  of  the  tribasic 
phosphate  to  one  of  carbonate:  3  Ca3(P04)2.CaC03. 

If,  by  treatment  with  dilute  hydrochloric  acid,  the  mineral 
constituents  are  entirely  dissolved  out  of  bone,  there  remains, 
a  substance  from  which  glue  (gelatin)  is  derived,  of  similar 
composition  to  collagen,  from  connective  tissue,  and  known  as 
ossein.  Neither  of  these  (ossein  or  collagen)  is  soluble  in  water 
or  in  dilute  acids. 

Bone  Marrow  is  of  two  sorts,  red  or  yellow.  The  red  marrow 
contains  erythrocytes,  fat,  lecithin,  protein  substance  consisting 
of  a  globulin,  a  nucleo-protein,  fibrinogen,  traces  of  albumin  and 
proteose. 

The  yellow  marrow  is  similar  in  composition,  except  that  it 
contains  fewer  erythrocytes,  more  fat  and  more  olein  in  the 
fat. 

Gelatin  is  made  by  hydrolysis  of  ossein  or  collagen  brought 
about  by  prolonged  boihng  with  dilute  mineral  acids.  Gelatin, 
if  first  treated  with  cold  water  till  soft,  may  be  dissolved  in  hot 
water.  The  solution  is  precipitated  by  mercuric  chloride, 
alcohol,  tannic,  and  picric  acids.  It  responds  but  feebly  to  the 
general  protein  reactions,  but,  by  digestion  with  either  pepsin  or 
trypsin,  compounds  are  obtained  analogous  to  those  resulting 
from  similar  protein  digestion. 


28o  PHYSIOLOGICAL  CHEMISTRY 

Gelatin  solutions  respond  to  the  biuret  test,  not  to  Millon's 
nor  to  the  Hopkins-Cole  test. 

Conjugated  Proteins. 

These  are  substances  which  contain  the  protein  molecule 
united  to  some  other  molecule  or  molecules  otherwise  than  as  a 
salt.  The  conjugated  proteins  which  we  shall  study  are  mucin, 
a  type  of  glyco-protein,  yielding  upon  decomposition  a  substance 
containing  a  carbohydrate  group;  caseinogen  (from  milk),  a 
phosphorus-containing  substance;  and  hemoglobin  (from  blood). 

The  glyco-protein,  mucin,  a  selected  type  of  this  class  of 
protein  substance,  occurs  in  various  forms  in  saliva,  in  urine,  bile, 
and  other  body  fluids.  The  mucin  substances  are  differentiated 
from  the  true  mucins,  according  to  Hammarsten,  by  the  fact  that 
the  latter  form  mucilaginous  or  ropy  solutions  by  the  aid  of  a 
trace  of  alkali,  from  which  they  are  precipitated  by  acetic  acid. 
The  precipitate  is  insoluble  in  excess  of  acid,  or  soluble  only  with 
great  difficulty. 

True  mucins  have  been  separated  and  examined  from  the 
secretion  of  the  submaxillary  glands,  from  snails,  from  mucous 
membranes  of  the  air  passages,  from  synovial  ffuid,  and  from  the 
navel  cord. 

Mucin  is  quite  readily  Converted  to  metaprotein  by  boiling 
with  dilute  acid,  and,  by  action  of  strong  acid,  will  yield  a 
number  of  the  simpler  amino  acids.  Mucin  itself  is  acid  in  re- 
action, but  there  is  no  evidence  that  it  has  power  to  form  salts. 

The  mucins  are  insoluble  in  pure  water,  but  dissolve  upon 
the  addition  of  traces  of  alkah.  The  solution  thus  obtained  will 
give  the  usual  color  reactions  for  the  proteins. 

The  action  of  mucin  as  a  factor  in  dental  caries,  formation  of 
gelatinous  plaques,  etc.,  will  be  discussed  under  SaUva. 

Caseinogen,  the  second  conjugated  protein  which  we  shall 
consider,  is  the  principal  nitrogenous  constituent  of  milk  and 
will  be  studied  as  such. 


PROTEINS  281 


Milk. 


Milk  is  the  characteristic  secretion  of  mammals  and  con- 
tains the  three  great  classes  of  food  material,  viz. :  the  proteins, 
carbohydrates,  and  fats.  The  fat  is  held  as  a  permanent  emul- 
sion in  so-called  milk  plasma. 

The  plasma  consists  of  water  holding  in  solution  caseinogen, 
albumin  with  a  trace  of  globulin,  milk  sugar  (lactose) ,  and  mineral 
salts. 

Specific  Gravity.  —  Milk  contains  two  different  sorts  of  sub- 
stances influencing  the  gravity;  first,  the  fat  being  lighter  than 
the  water  tends  to  decrease  the  gravity;  second,  the  sohds  not 
fat  which  are  heavier  than  water  tend  to  increase  the  gravity  of 
the  milk.  Consequently,  it  may  happen  that  a  very  poor  milk 
and  a  very  rich  milk  will  have  the  same  specific  gravity;  e.g.,  the 
normal  gravity  of  whole  milk  is  about  1.031,  while  the  gravity 
of  skim  milk  will  be  about  1.035  or  1-036,  and  that  in  which  cream 
occurs  in  large  amount  may  be  as  low  as  1.015  or  1.020.  It  can 
be  easily  seen  that  starting  with  whole  milk,  the  addition  of 
cream  or  the  addition  of  water  wiU  both  alike  reduce  the  gra\dty. 
Hence,  taken  alone,  the  gra\dty  tells  little  or  nothing  as  regards 
the  quaHty  of  milk;  but,  if  the  gravity  is  taken  together  with 
the  fat  content,  the  two  factors  give  oftentimes  sufficient  infor- 
mation. 

The  relation  between  the  gravity  of  the  fat  and  the  total 
soHds  is  approximately  constant,  and  the  following  formula 
will  give  the  amount  of  total  sohds  usually  within  o.ib  or  0.15 
of  1%. 

-  Total  solids  =  ^^^^^  +  ^£^  +  0.46. 
.5  4 

Reaction.  —  The  reaction  of  cow's  milk,  when  perfectly 
fresh,  is  amphoteric  to  htmus;  i.e.,  it  will  both  redden  blue  litmus 
paper  and  turn  red  Htmus  blue  at  the  same  time.     This  double 


282  PHYSIOLOGICAL   C/IEMLSTRY 

reaction  is  due  to  the  presence  of  various  salts,  probably  the 
acid  and  alkaline  phosphates. 

Cow's  milk  is  acid  to  phenolphthalein,  and  this  acidity 
naturally  increases  by  the  multiplication  of  various  acid-forming 
bacteria,  which  produce  lactic  acid  by  hydrolysis  of  the  milk 
sugar.  When  the  acid  strength  has  increased  sufficiently,  the 
caseinogen  is  decomposed,  and  casein  is  produced  and  pre- 
cipitated. 

This  casein  constitutes  the  curd,  and  the  process  is  the 
ordinary  souring  of  milk. 

Lactic  acid  is  not  the  only  acid  produced  in  the  spontaneous 
fermentation  of  milk,  as  traces  of  formic,  acetic,  butyric,  and 
succinic  acids  have  been  demonstrated  by  different  investiga- 
tors. 

The  degree  of  acidity  of  milk  is  conveniently  determined  as 
suggested  by  W.  Thorner  (Chem.  Zeit.,  1891,  page  1108,  abst. 
analyst  XVI,  200),  10  c.c.  of  milk  with  an  equal  volume  of  water 
and  a  few  drops  of  phenolphthalein  as  indicator,  are  titrated  with 
N/io  alkali  and  every  tenth  of  a  degree  of  alkali  used  is  con- 
sidered as  representing  one  "degree"  of  acidity. 

By  experimenting  on  samples  kept  under  various  con- 
ditions, Thorner  found  that  milk  coagulates  on  boiling  when 
the  acidity  reaches  23°.  Adopting  20°  as  the  permissible  limit 
of  acidity,  he  proposes  the  following  test:  10  c.c.  of  milk,  20  c.c. 
of  water,  a  few  drops  of  indicator,  and  2  c.c.  of  decinormal  alkali 
are  thoroughly  mixed;  if  any  red  color,  however  weak,  results, 
the  milk  will  not  coagulate  upon  boiling.* 

This  method  is  given  partly  for  its  own  sake  and  partly  be- 
cause exactly  the  same  method  is  used  by  Dr.  Eugene  S.  Talbot 
of  Chicago  and  many  others  for  the  determination  of  acidity  of 
urine.  By  slight  modification  it  may  be  used  for  saliva.  The 
record  of  slight  amounts  of  acidity  made  in  degrees  in  this  way 
has  several  practical  points  in  its  favor. 

*  From  Allen's  Commercial  Organic  Analysis,  Vol.  4. 


PROTEINS 


283 


Casein  is  the  principal  protein  found  in  milk.  It  exists  in 
combination  with  calcium  salts  as  caseinogen.  This  combina- 
tion is  broken  up  and  the  casein  precipitated  by  the  action  of 
rennin  and  other  enzymes,  by  acids,  and  by  certain  inorganic 
salts. 

Casein  is  classified  as  a  pseudo-nucleo-albumin.  The  nucleo- 
proteins,  so  named  because  true  nuclein  may  be  obtained  from 
them,  are  constituents  of  the  cell  nuclei,  and  differ  in  composi- 
tion from  ordinary  proteins  by  containing  from  0.5  to  1.6%  of 
phosphorus.  Casein  from  cow's  milk  contains,  according  to 
Hammarsten,  0.85%  of  phosphorus.  It  has  been  classified  as 
a  pseudo-micleo-aXhumm  because,  upon  digestion  with  pepsin, 
pseudo-nuclein  rather  than  true  nuclein  is  obtained. 

Casein  is  practically  insoluble  in  water,  but  dissolves  readily 
in  dilute  alkaline  solutions.  Its  precipitation  as  curd  is  de- 
pendent upon  the  presence  of  calcium  salts. 

Lactalbumin  is  the  only  other  protein  substance  worthy  of 
note  in  milk.  This  may  be  found  in  the  filtrate  after  separat- 
ing the  casein.  The  total  proteins  contained  in  human  milk 
average  from  1.5  to  2.5  per  cent  while  in  cow's  mi  k  the  proteins 
are  3.0  to  4.5  per  cent.  This  difference,  together  with  the  vari- 
ation of  reaction  and  sugar-content,  makes  it  necessary  to 
"modify"  cow's  milk  when  it  is  used  as  an  infant  food. 

The  modification  usually  consists  in  the  addition  of  lime- 
water  (to  change  the  reaction) ,  of  water  (to  reduce  percentage  of 
proteins),  and  of  cream  and  milk-sugar  (to  increase  fat  and 
lactose). 

The  following  table  shows  comparative  composition: 


- 

Reaction. 

Total 
solids. 

Proteins. 

Sugar. 

Fat. 

Ash. 

Human  milk. . 
Cow's  milk. .-. 

Alkaline 

Acid 

13.00% 
14.00% 

2.70% 
4-i57o 

6.10% 
4  90% 

4.00% 
4.25% 

0.2D% 

0.70% 

284  ♦  PHYSIOLOGICAL  CHEMISTRY 

Fat.  —  The  fat  of  milk  exists  as  microscopic  globules  appar- 
ently inclosed  in  a  protein-like  membrane  separating  substance, 
the  presence  of  which  seems  a  necessary  theory  to  account  for 
the  behavior  of  milk  fat  toward  various  solvents  such  as  ether. 
The  milk  fat  or  butter  fat  consists  largely  of  olein  and  palmitin 
with  a  slight  amount  of  butyrin  and  traces  of  sev'eral  other  fatty 
acids. 

Milk,  as  has  already  been  stated,  undergoes  lactic  acid 
fermentation  readily  and  this  may  be  induced  by  a  considerable 

number  of  microorganisms.  It  is 
not,  however,  liable  to  alcoholic 
fermentation  except  under  peculiar 
circumstances.  Alcoholic  fermen- 
tation may  be  induced  by  certain 
ferments,  such  as  the  Kephir  grain 
used  quite  largely  in  the  East,  the 
product  being  known  as  Kumiss 
or  milk  wine.  Kumiss  originally 
was  produced  from  mare's  milk, 
Fig.  iS.  .Milk  and  Colostrum.  b^t  the  name  has  also  been  appUed 
to  any  milk  which  has  undergone  alcoholic  fermentation. 

Colostrum  is  a  peculiar  substance  occurring  at  the  very 
earliest  stages  of  lactation.  Its  specific  gravity  is  considerably 
higher  than  that  of  milk,  being  1.040  to  1.060.  It  contains 
much  more  protein  substance  and  is  characterized  by  the  pres- 
ence of  granular  corpuscles  known  as  colostrum  corpuscles. 
(Fig.  18.) 

Derived  Proteins. 

Meta-proteins  —  Acid  Meta-protein.  —  The  digestive  action 
of  the  gastric  juice  on  protein  substances  is  the  formation 
of  an  acid  meta-protein,  formerly  called  acid  albuminate. 
The    meta-proteins   are    characterized  by  the    fact    that    they 


PROTEINS  285 

are  precipitated  on  neutralization  and  are  not  coagulated  by 
heat.  They  may  also  be  precipitated  by  saturation  with  com- 
mon salt. 

The  AlkaU  Meta-protein  or  alkali  albuminate  is  the  stronger 
of  these  two  classes  of  compounds  when  considered  from  a  chem- 
ical standpoint;  that  is,  the  reactions  are  more  marked,  and  some 
compounds  will  be  formed  with  the  alkaU  albuminate  which  are 
not  produced  when  the  acid  albuminate  is  treated  in  a  similar 
way.  The  acid  meta-protein  from  the  digestion  of  meat  is  known 
as  syntonin. 

The  Proteoses  (albumoses)  may  be  considered  as  the  next 
well-defined  protein  product  of  protein  digestion  following  the 
albuminate.  That  is,  leaving  out  the  many  intermediate  prod- 
ucts between  which  sharp  hues  of  demarcation  cannot  be  drawn, 
the  decomposition  of  albumin  brought  about  by  enzymes  or 
digestive  ferments  gives,  first,  acid  albumin;  second,  albumose; 
and  third,  peptone.  Albumose  may  be  taken  as  a  type  of  this 
second  class  of  digestive  products.  Other  proteoses,  such  as 
globulose,  etc.,  are  the  substances  derived  from  other  proteins 
at  a  corresponding  point  of  decomposition  or  peptic  digestion. 
Albumose  may  be  coagulated  by  heat  at  a  temperature  ranging 
upwards  from  56°  C,  but,  unlike  albumin,  as  the  temperature 
approaches  the  boiling-point  the  albumose  goes  again  into  solu- 
tion, and  at  a  boihng  temperature  may  be  separated  from  albumin 
by  filtration.  As  the  filtrate  cools,  albumose  will  again  precipi- 
tate. The  albumose  is  also  precipitated  by  nitric  acid,  by  ferro- 
cyanide  of  potassium  and  acetic  acid  (the  precipitate  in  both  cases 
being  dissolved  by  heat),  and  the  other  general  protein  precipi- 
tates. The  biuret  test  gives  a  distinctive  color  with  proteoses 
and  peptones,  it  being  a  marked  reddish  shade  rather  than  the 
violet  or  blue  obtained  with  other  proteins. 

Peptones  are  the  final  products  of  peptic  digestion  of  the 
proteins.  They  are  soluble  substances  which  give  the  biuret 
test  similarly  to  the  proteoses,  but  are  not  precipitated  by  heat, 


286  PHYSIOLOGICAL   CHEMISTRY 

by  nitric  acid,  by  potassium  ferrocyanide  and  acetic  acid,  nor 
by  saturation  with  ammonium  sulphate. 

Peptides.  —  The  peptides  are  the  simpler  forms  of  the  pep- 
tones, many  of  them  being  complex  amino  acids.  Upon  decom- 
position or  hydrolytic  splitting  of  peptide,  the  simpler  amino 
acid,  which  is  without  the  protein  characteristics,  results. 

BLOOD    AND    MUSCLE. 
Blood. 

The  blood,  carrying  oxygen  and  other  forms  of  nutrition  to 
all  parts  of  the  body,  and  returning  carbon  monoxide  and  the 
waste  products  of  cellular  activity,  is  an  exceedingly  complex 
substance.  The  composition  of  the  blood  itself,  however,  may 
be  grossly  described  as  a  fluid  (plasma)  carrying  in  suspension 
the  cellular  constituents,  red  and  white  corpuscles.  The  plasma 
contains  solid  matter  to  the  extent  of  about  8.9%.  This  is 
largely  protein,  consisting  of  serum  globuhn,  serum  albumin, 
a  slight  amount  of  nucleoprotein,  and  fibrinogen;  also  a  fibrin 
ferment,  thrombase  or  thrombin,  by  the  action  of  which  the 
fibrin  is  separated  as  a  "clot"  which  mechanically  carries  down 
the  corpuscles.  As  the  clot  contracts,  the  "serum"  separates 
as  a  clear,  amber-colored  hquid,  consisting  of  serum  globulin 
(paraglobuhn) ,  serum  albumin,  and  the  fibrin  ferment. 

Fibrin.  —  The  fibrin  may  be  obtained  free  from  corpuscles 
by  whipping  fresh  blood.  Under  this  treatment  the  fibrin 
separates  as  shreds,  while  the  remaining  fluid  constitutes  "de- 
fibrinated  blood."  The  presence  of  hme-salts  is  essential  to 
the  coagulation  of  the  blood,  i.e.,  the  decomposition  of  fibrin- 
ogen and  separation  of  fibrin,  in  much  the  same  way  as  in  the 
decomposition  of  caseinogen  and  precipitation  of  casein  from 
milk. 

Fibrin,  as  usually  obtained,  is  in  the  form  of  brown,  stringy, 
and  "fibrinous"  masses,  which  are  kept  under  glycerin  for  labor- 


PLATE  VII.- PHYSIOLOGICAL  CHEMISTRY. 


Fig.  I. 
Edestin. 


Fig.  3. — Fat  Crystals. 
A,  Butter  Crystals;  B,  Lard  Crystals. 


Fig.  s. 

A,  Human  Blood;  B,  Horse  Blood; 

C,  Dog  Blood. 


Fig.  2. 
Teichmann's  Hemin  Crystals. 


Fig.    4- 
A,  Fat  Acid;  B,  Cholesterin. 


Fig.  6. 
A,  Frog  Blood;  B,  Chicken  Blood; 
C,  Fish  Blood. 


BLOOD  AND  MUSCLE  287 

atory  use.  It  is  insoluble  in  water  or  alcohol.  In  dilute  acid, 
(HCl),  or  alkali  solutions,  it  swells  and  ultimately  dissolves, 
although  it  may  be  several  days  before  solution  is  effected.  The 
fibrins  from  the  blood  of  different  animals  differ  in  composition, 
as  indicated  by  marked  differences  in  solubility. 

The  chemistry  of  the  red  and  white  corpuscles  is  more  complex 
and  not  so  well  known  as  the  chemistry  of  the  plasma,  which 
we  have  considered.  The  red  corpuscles  consist  of  a  frame  of 
protoplasm,  also  called  stroma,  which  contains  lecithin,  choles- 
trin,  nucleoalbumin,  and  a  globulin.  (Hammarsten.)  Upon 
and  all  through  the  stroma  is  the  hemoglobin,  which,  together 
with  its  oxygen  compound  oxyhemoglobin,  is  responsible  for 
the  color  of  the  blood.  Oxyhemoglobin  may  be  obtained  as 
silky,  transparent  crystals  of  blood-red  color. 

From  hemoglobin  may  be  derived  the  blood  pigment  hemo- 
chromogen,  containing  iron,  and  this  by  oxidation  is  converted 
into  hematin.  The  iron  from  the  blood  may,  by  decomposi- 
tion of  the  pigment  and  subsequent  combination  with  sulphur 
(FeS),  cause  discoloration  of  teeth.  This  is  the  theory  of  Dr. 
E.  C.  Kirk,  and  in  the  author's  opinion  is  perfectly  sound,  and 
far  more  probable  than  other  explanations  which  have  been 
offered,  but  which  do  not  recognize  the  formation  of  a  sulphur 
compound. 

The  form  of  the  red  corpuscle  is  that  of  a  biconcave  disk 
without  nucleus;  by  action  of  water  it  becomes  swollen,  and 
the  hemoglobin  may  be  washed  away,  leaving  the  "stroma." 
The  diameter  of  the  red  corpuscles  of  human  blood  is  about 
1/3200  of  an  inch.  Of  the  domestic  animals,  the  corpuscles  of 
the  dog  approach  most  nearly  to  the  measurement  of  the  human. 
The  sheep,  horse,  and  ox  have  smaller  corpuscles  than  man, 
while  those  of  birds,  cold-blooded  animals,  and  reptiles  are 
larger  (see -Plate  VII,  Figs.  5  and  6). 

The  white  corpuscles  are  rather  larger  than  the  red,  and 
occur  in  much  smaller  numbers,  a  cubic  millimeter  containing 


288  PHYSIOLOGICAL  CHEMISTRY 

about  5,000,000  red  to  7500  white.  The  white  corpuscles  pre- 
sent a  much  greater  diversity  of  character  than  do  the  red. 
They  contain  one  to  four  nuclei,  and  are  capable  of  amoeboid 
movements.  The  white  corpuscles  are  also  called  leucocytes, 
aggregations  of  which  constitute  pus.  The  leucocytes  are  di- 
vided histologically  into  various  classes,  —  lymphocyte,  neutro- 
philes,  eosinophiles,  etc.,  —  according  as  they  are  acted  upon 
by  different  staining-fluids  or  fulfill  some  particular  office;  but 
these  are  not  to  be  distinguished  chemically. 

Hemoglobin.  —  Hemoglobin  may  be  separated  from  blood 
by  shaking  with  a  little  ether  and  water  and  allowing  to  stand 
twelve  hours  on  ice;  or  sometimes  crystals  may  be  obtained  by 
simply  allowing  a  drop  of  defibrinated  blood  to  partially  dry  on 
a  microscope  slide.  The  hemoglobin  from  different  animals 
crystallizes  in  more  or  less  distinctive  forms;  for  example,  from 
human  blood  the  crystals  will  be  diamond  shape  or  rectangular, 
from  guinea  pigs,  tetrahedrons  or  octahedrons  resembling  the 
crystals  of  white  arsenic,  and  from  squirrels,  six-sided  plates. 

The  composition  of  hemoglobin  has  been  given  as  96% 
globin  (a  histone),  and  the  remainder  hemochromogen. 

Hemoglobin  forms  compounds  with  various  gaseous  sub- 
stances and  furnishes  a  good  example  for  the  study  of  the  law 
of  mass  action.  In  the  lungs  excess  of  oxygen  slowly  drives 
other  gases,  particularly  carbon  dioxide,  out  of  combination, 
and  forms  oxyhemoglobin,  while  in  the  capillaries  excess  of 
carbon  dioxide  in  venous  blood  replaces  the  oxygen.  Hydrogen 
sulphide,  nitric  oxide,  nitrous  oxide,  and  carbon  monoxide  all 
form  compounds  with  hemoglobin  of  various  degrees  of  stabihty, 
the  most  stable  being  formed  by  carbon  monoxide  which  acts  by 
preventing  the  formation  of  oxyhemoglobin.  Blood  containing 
carbon  monoxide  hemoglobin  is  of  a  bright-red  color,  which 
darkens  in  the  air  much  more  slowly  than  ordinary  blood. 

Hematin  is  an  oxidation  product  of  hemoglobin  and  has 
been  assigned  the  formula  C32H32N404Fe. 


BLOOD  AND  MUSCLE  289 

Hemin,  or  Teichmann's  hemin  crystals,  is  the  hydrochloric 
acid  compound  of  hematin.  (See  Exp.  239,  page  414,  also 
Plate  VII,  Fig.  2.) 

Muscle. 

The  chemistry  of  muscle  is  complex.  It  changes  rapidly 
upon  the  death  of  the  afiimal,  so  much  so  that  the  liquid  which 
may  be  expressed  from  living  muscle  (or  from  muscle  frozen 
immediately  upon  the  death  of  the  animal)  has  been  called 
muscle  plasma,  in  distinction  from  the  fluid  obtained  in  the 
same  manner  from  dead  muscle,  which  is  called  muscle  serum. 
The  chemical  reactions  of  these  solutions  differ,  due  to  the 
formation  of  sarcolactic  acid  in  the  dead  muscle.  The  proteins 
differ  in  certain  respects. 

The  two  proteins  of  muscle  plasma  are  given  by  Halliburton 
as  paramyosinogen  25%,  and  myosinogen  75%.  Of  these  the 
paramyosinogen  seems  to  be  a  globulin,  while  the  myosinogen, 
having  many  of  the  properties  of  a  globulin,  is  soluble  in  pure 
water  and  is  rather  a  mother  protein  from  which  the  clot  from 
muscle  serum  is  produced.  The  protein  of  the  muscle  clot  is 
known  as  myosin  or  myogen.  Myosin  may  be  precipitated  from 
muscle  serum  by  saturation  with  sodium  chloride  or  magnesium 
sulphate.  It  has  many  of  the  properties  of  the  globulins,  but 
differs  in  the  very  important  particular  of  not  being  precipitated 
by  dialyzation.  Among  the  more  important  extractive  bodies 
obtained  from  muscle  are  creatin,  carnin,  inosite,  glycogen,  and 
lactic  acid.  Creatin  is  a  xanthin  body,  being  chemically  a 
methyl-guanidin-acetic  acid,  which  may  appear  in  the  urine  as 
creatinin.  -  (Creatinin  is  creatin  minus  water.) 

Carnin  is  a  white  crystalline  substance  obtained  from  meat 
extract  and  converted  by  oxidation  induced  or  produced  by 
nitric  acid,  chlorine  or  bromine  into  hypoxanthin  or  sarkin.  Its 
chemical'constitution  is  not  positively  known. 


290  PHYSIOLOGICAL  CHEMISTRY 

Inosite,  CeHiaOe  +  H2O,  is  a  hexahydroxybenzene,  C6H6(OH)(5 
+  H2O.  It  has  a  sweet  taste,  and  was  formerly  erroneously 
classed  with  the  carbohydrates.  It  is  capable  of  yielding  lactic 
and  butyric  acids  (?). 

Glycogen  occurs  in  slight  amounts  in  muscle,  but  decomposes 
after  death,  with  formation  of  a  reducing  sugar.  (Compare 
page  263.) 

Lactic  Acid  is  a  constituent  not  only  of  muscle  but  also  of 
various  glands,  of  the  bile,  and  of  blood.  For  the  chemistry 
of  this  substance,  see  page  222. 


PART   VI I. 

DIGESTION. 

CHAPTER  XXXIII. 

SALIVA  PROPERTIES   AND   CONSTITUENTS. 

The  saliva  is  a  mixed  secretion  from  the  parotid,  submaxil- 
lary, and  sublingual  glands,  together  with  a  slight  amount 
obtained  from  the  smaller  buccal  glands.  The  chemical  com- 
position of  the  secretion  from  these  various  sources  differs  con- 
siderably, but  from  a  dental  standpoint  we  are  much  more 
interested  in  the  mixed  saUva  and  its  constituents  than  the 
differences  in  the  products  of  the  various  glands.  The  notable 
differences  are  that  the  mucin  is  practically  wanting  in  the 
parotid  saHva.  The  alkaline  salts  seem  to  be  in  smaller  pro- 
portion in  the  parotid  saUva  than  in  the  other  two.  Potassium 
sulphocyanate  is  a  constituent  of  all  varieties  of  sahva,  although 
more  constantly  present  in  the  submaxillary  and  in  the  subhiigual 
than  in  the  parotid.  The  parotid,  on  the  other  hand,  contains 
a  larger  proportion  of  dissolved  gases.  The  data  on  the  com- 
position of  these  varieties  differ  to  a  considerable  extent  and 
comparisons  are  not  wholly  satisfactory. 

The  mixed  sahva  contains,  according  to  Professor  Michaels, 
all  the  salts  of  the  blood  which  are  dialyzable  through  the  salivary 
glands,  and  iience  furnishes  a  rehable  index  of  metaboHc  proc- 
esses which  are  being  carried  on  within  the  system.  In  order 
for  this  fact  .to  be  of  practical  value,  two  things  are  obviously 
of  prime  importance:  First,  methods  of  analysis  which  are  not 
too  comphcated  and  which  are  at  the  same  time  conclusive; 

291 


292  DIGESTION 

second,  a  knowledge  regarding  the  source  of  the  various  con- 
stituents found  which  will  enable  us  to  make  a  rational  inter- 
pretation of  the  results  obtained.  In  both  of  these  fundamentals 
we  are  very  much  hampered  by  lack  of  knowledge;  as  yet  there 
is  much  to  be  desired  in  the  way  of  practical  cHnical  tests  for 
the  various  salivary  constituents,  and  very  much  to  be  learned 
as  to  their  meanings  in  order  to  make  deductions  which  shall 
be  conclusive.  We  are  led  to  beUeve  from  the  work  of  an 
increasing  number  of  specialists  that  this  subject  of  salivary 
analysis  promises  much  and  is  certainly  worthy  of  careful 
investigation. 

The  quantity  of  saliva  secreted  in  twenty-four  hours  is  vari- 
ously estimated  from  a  few  hundred  to  1500  c.c;  1200  to  1500 
is  the  more  probable  amount.  The  quantity  is  diminished  in 
fevers,  severe  diarrhea,  diabetes,  and  nephritis,  by  fear  and 
anxiety,  and  by  the  use  of  atropine.  It  is  increased  by  smoking, 
by  mastication,  by  the  use  of  mercury,  potassium  iodide,  or 
pilocarpin.  The  flow  of  saliva  is  also  increased  by  action  of  the 
sympathetic  nervous  system,  during  pregnancy,  and  by  local 
inflammatory  process. 

Physical  Properties.  —  The  physical  properties  of  saliva  in- 
clude its  appearance,  specific  gravity,  reaction,  color,  and  odor. 

Appearance.  —  The  appearance  is  clear,  opalescent,  frothy, 
or  cloudy;  normal  saliva  is  usually  opalescent.  It  may  become 
turbid  by  precipitation  of  lime-salts  caused  by  the  escape  of 
carbon  dioxide. 

Specific  Gravity.  —  Specific  gra\ity  ranges  from  1.002  to  1.009, 
the  total  solids  being  only  from  0.6  to  2.5  per  cent. 

Reaction.  —  The  reaction  is  normally  alkaline  to  litmus- 
paper  or  to  lacmoid.  Normal  saliva,  however,  fails  to  give 
an  alkaline  reaction  with  phenolphthalein,  due  to  the  presence 
of  free  carbon  dioxide,  which  may  be  present  to  the  extent  of 
nineteen  parts  in  a  hundred,  by  volume.  If  the  sample  be 
subjected  to  even  a  shght  degree  of  heat  the  acid  gas  is  expelled; 


SALIVA   PROPERTIES  AND  CONSTITUENTS  293 

then  the  usual  pink  color  may  be  obtained  with  this  indicator. 
SaHva  may  be  acid  upon  fasting,  particularly  before  breakfast 
and  also  after  much  talking.  Acid  conditions  may  exist  which 
are  local  in  their  character  and  due  to  lactic  acid  fermentation. 
Acid  sahvas  may  also  be  met  with  in  cases  of  rheumatism, 
mercury  salivation,  and  diabetes.  By  exercise  of  the  glands, 
as  during  the  chewing  of  food,  the  alkalinity  is  increased;  often- 
times the  reaction  changes  from  faintly  acid  to  alkaline  during 
this  process,  the  proportion  of  alkahne  salts  becoming  greater, 
although  the  total  soHds  as  a  whole  are  slightly  diminished. 
This  fact  of  the  change  in  the  reaction  from  acid  to  alkaUne 
has  been  explained  by  ascribing  the  acidity  to  fermenting 
particles  in  the  mouth;  the  continued  process  of  chewing  and 
swallowing  washes  this  away,  or,  in  other  words,  the  change  in 
reaction  is  a  mechanical  one  rather  than  a  change  of  the  chemical 
composition  of  the  secretion.  This  explanation  seems  to  be  a 
superficial  one  and  without  sufficient  experimental  foundation. 

The  acidity  of  saHva,  as  indicated  at  the  bottom  of  page  292, 
is  referred  to  the  behavior  of  the  saliva  to  phenolphthalein, 
and  is  in  large  part  due  to  the  presence  of  free  carbon 
dioxide. 

The  sources  of  carbon  dioxide  in  saUva  are  probably  three: 
carbon  dioxide  dialyzed  through  the  salivary  glands,  traces 
from  carbohydrate  fermentation,  and  more  or  less  absorbed 
from  contact  with  expired  air. 

The  sahva  obtained  by  chewing  paraffin  (a  process  calcu- 
lated to  furnish  the  maximum  amount  from  the  last  two  sources), 
may  yield  several  times  the  amount  of  free  carbon  dioxide  that 
another  sample  taken  from  the  same  patient  by  a  saHva  ejector 
will  give.     - 

Acidity  of  saUva  may  be  temporary  when  it  may  be  entirely 
removed  by  .drawing  air  through  the  heated  (not  boiled)  sample. 
The  permanent  acidity  may  be  determined  by  titration  of  the 
sample  after  removal  of  carbon  dioxide. 


294 


DIGESTION 


The  apparatus  pictured  in  Fig.  19  has  been  used  by  the 
author  for  this  acidity  determination. 

The  air  is  drawn  from  left  to  right  first  through  a  potash 
bulb  (A)  to  absorb  atmospheric  carbon  dioxide,  next  through 


Fig.  19. 

10  c.c.  of  saliva  diluted  with  20C.C.  of  water  contained  in  a 
small  Soxhlet  flask  (B)  whereby  the  carbon  dioxide  from  the 
saliva  is  carried  through  the  "  test-tube  "  condenser  and  col- 
lected in  baryta  water  in  the  Erlenmeyer  flask  (C)  at  the  left. 
This  in  turn  is  connected  with  a  suction  pump  or  aspirator. 


SALIVA    PROPERTIES  AND  CONSTITUENTS 


295 


The  "  drip  cup  "  {D)  has  been  found  necessary  when  working 
with  very  viscid  samples.  The  thistle  tube  (E)  holds  water  for 
maintaining  the  volume  in  (B)  if  the  condenser  is  not  used. 


Fig.  20.     Colorimeter. 


The  amount  of  free  carbon  dioxide  may  be  determined  by 
adding  a  standard  carbonate  solution  (N/ioo  Na2C03)  to  a 
volume  of  baryta  water  equal  to  that  used  in  the  Erlenmeyer 
flask  and  then  comparing  the  degree  of  turbidity  obtained. 
This  may  be  done  by  viewing  through  flat-bottom  tubes  (shell 


296  DIGESTION 

tubes)  of  about  20  c.c.  capacity,  or,  in  many  cases,  better,  by 
use  of  the  Duboscq  colorimeter  used  for  determination  of  am- 
monia (Fig.  20,  page  295),  or  better  still  by  the  use  of  the 
nephelometer  made  with  the  Duboscq  colorimeter  after  the 
method  of  Dr.  Bloor.  (Journal  of  Biological  Chemistry,  vol. 
22,  p.  145,  1915.)  This  apparatus  may  also  be  used  to  advan- 
tage in  the  determination  of  calcium  in  saliva,  or  acetone  bodies 
in  urine.  The  nephelometer  differs  from  the  Duboscq  color- 
imeter in  that  it  makes  use  of  reflected  rather  than  transmitted 
Ught. 

The  following  method  for  the  determination  of  temporary 
acidity  is  also  recommended.  Force  air  free  from  carbon  diox- 
ide through  a  measured  volume  of  saliva  (20  c.c.)  which  has  been 
previously  mLxed  with  an  equal  volume  of  water,  then  into 
baryta-water  containing  a  little  barium  chloride,  using  a  Folin 
absorption  tube  (Fig.  25,  page  310).  The  carbon  dioxide  thus 
becomes  fixed  as  barium  carbonate.  Transfer  the  precipitated 
carbonate  to  a  filter  paper  and  wash  free  from  chlorine.  Dis- 
solve off  paper  in  dilute  hydrochloric  acid,  collecting  filtrate  in 
porcelain  dish.  Evaporate  to  dryness  over  water  bath  and 
titrate  chlorine  with  N/20  silver  nitrate,  i  c.c.  N/20  AgNOs  = 
.0010917  gram  of  COo. 

Another  method  consists  in  passing  carbon  dioxide  as  above, 
into  a  measured  volume  of  standardized  baryta-water  (N/20) 
and  titrating  excess  of  barium  hydroxide  with  N/20  oxalic  acid. 
The  end  point  is  determined  by  "spotting"  onto  fresh  tumeric 
paper.  When  the  paper  ceases  to  turn  brown-red  the  end  of 
the  reaction  has  been  reached. 

Permanent  acidity  is  of  comparatively  rare  occurrence  and 
is  due  either  to  the  presence  of  acid  salts,  such  as  NaH2P04,  or 
slight  amount  of  organic  acids  possibly  combined  as  acid  meta- 
protein.  This  acidity  and  its  cUnical  significance  is  at  present 
under  investigation. 

Color.  —  Saliva   is   usually   colorless   when   fresh,   but   upon 


SALIVA    PROPERTIES  AND   CONSTITUENTS  297 

standing  for  twenty-four  hours  may  assume  various  tints, 
which  are  developed  from  constituents  derived  from  bile.  (Pro- 
fessor Michaels.)  Sahva  may  be  colored  red  or  brown  by  the 
presence  of  blood  or  blood  pigments,  but  in  such  cases  the 
source  of  the  color  is  usually  local  and  easily  discovered. 

Odor.  —  Normal  sahva  is  practically  odorless.  In  cases  of 
pyorrhea  there  is  usually  a  peculiar  fetid  odor  easily  recognized. 
In  other  pathogenic  conditions  the  odor  may  be  shghtly  am- 
moniacal,  or  occasionally  resemble  the  odor  of  acetone  or 
garhc. 

Constituents.  —  We  should  here  distinguish  carefully  be- 
tween sahva  proper  and  sputum.  The  constituents  of  sputum 
are  derived  from  the  air-passages  rather  than  from  the  sahvary 
glands,  and  are  not  at  present  under  consideration.  Among 
the  normal  constituents  of  sahva  are  included  mucin,  albumin, 
ptyahn,  also  oxidizing  enzymes,  ammonium  salts,  nitrites, 
potassium  sulphocyanate,  alkahne  phosphates,  and  chlorides, 
with  traces  of  carbonates;  and,  in  the  sediment,  epithehum 
cells,  occasional  leucocytes,  and  fat  globules.  The ,  abnormal 
constituents  wi  1  include  glycogen,  urea,  dextrin,  rarely  sugar, 
cholesterin,  derivatives  from  bile,  lecithin,  xanthin  bodies  or 
alkahne  urates,  acetone,  lactic  acid,  and  crystalline  elements 
resulting  from  insufficient  oxidation  or  perverted  glandular' func- 
tion. These  latter  are  recognizable  by  the  micropolariscope. 
Mercury  and  lead  may  also  be  found  in  sahva  in  cases  of  poison- 
ing by  salts  of  these  metals. 

Mucin.  —  The  secretion  from  the  parotid  gland  contains 
practically  no  mucin,  but  the  subhngual  sahva  contains  large 
amounts.  Mucin  is,  according  to  Simon,  the  most  important 
constituent  of  the  sahva,  not  excepting  ptyahn.  The  various 
glands  contributing  salivary  mucin  do  not  in  all  probabihty 
furnish  just  the  same  kind  of  protein;  moreover,  the  mucin 
from  different  individuals  seems  to  vary  in  composition  and 
properties,  some  yielding  more  abundant  acid  decomposition 


298  DIGESTION 

products  than  others  (see  article  by  W.  D.  Miller,  in  Dental 
Cosmos  for  November,  1905),  while,  according  to  Professor 
Michaels,  the  mucin  varies  much  in  the  same  individual  in 
health  and  disease.  The  changes  in  the  characteristics  of 
salivary  mucin  have  been  studied  but  Httle,  and  the  investiga- 
tion of  these  changes,  as  indications  of  diathetic  states,  promises 
much. 

An  excess  of  mucin  in  the  saHva  tends  to  an  increase  of 
bacterial  growth,  from  the  fact  that  it  furnishes  increased 
facilities  for  multipKcation;  it  has  been  suggested  that  it  may 
also  give  rise  to  mucic  acid,  and  thereby  be  a  possible  factor 
in  tooth  erosion.  (Dr.  G.  W.  Cook  in  Dental  Review,  May, 
1906,  page  461.) 

Alhmnin.  —  Albumin  is  present  in  very  small  quantities, 
increased  during  mercurial  ptyalism,  usually  in  cases  of  pyor- 
rhea, and,  according  to  some  authorities,  in  various  albumi- 
nurias. It  may  be  detected  by  usual  methods  after  the  separa- 
tion of  mucin. 

"  According  to  Vulpian,  the  quantity  of  albumin  is  increased 
in  the  saliva  of  albuminurics  of  Bright's  disease.  The  saKva 
of  a  patient  with  parenchymatous  nephritis  had  mucin  0.253 
and  albumin  0.182  per  cent.  The  saHva  of  another  patient, 
with  albuminuria  of  cardiac  origin,  contained  mucin  0.45, 
albumin  0.145  per  cent.  In  a  healthy  man  there  was  found 
mucin  0.320,  albumin  0.05  per  cent.  This  fact  has  been  con- 
firmed by  Pouchet,  who  found  these  substances  in  greater 
quantities."  * 

Ptyalin.  —  Ptyalin  is  the  principal  ferment  of  the  saHva ;  it 
converts  starch,  by  hydrolysis  through  the  various  dextrins 
(page  263),  to  maltose.  The  maltose  in  turn  is  converted  into 
glucose  by  a  second  ferment,  known  as  maltase,  which  exists 
in  saliva  in  very  small  quantities. 

*  Dr.  Joseph  P.  Michaels.  S.  S.  White's  reprint  of  paper  read  before  Inter- 
national Dental  Congress,  Paris,  1900. 


SALIVA   PROPERTIES  AND  CONSTITUENTS  299 

The  activity  of  ptyalin  is  greatest  at  a  temperature  of  40°  C. 
Very  faintly  acid  saliva  is  the  best  media.  Neutral  and  faintly 
alkahne  salivas  are  next  in  order. 

The  amylolytic  power  of  a  given  sample  of  saliva  may  be 
determined  by  the  action  on  dilute  starch  paste.  In  making 
comparative  tests  it  is  essential  that  the  conditions  under  which 
the  ptyahn  is  allowed  to  act  should  be  exactly  the  same,  es- 
pecially as  regards  the  temperature  and  duration  of  the  process. 
A  slight  variation  in  the  strength  of  the  starch  solution  is  of  no 
consequence,  as  starch  is  supposed  to  be  in  excess.  (See  Exp. 
245  on  page  416,  also  method  on  page  313.) 

Proteolytic  Eiizyjnes. —  Vipon  incubation  with  certain  prod- 
ucts of  protein  digestion  (dipeptides)  proteolytic  action  of 
saliva  has  been  noted;  whether  this  action  is  due  to  an  enzyme 
or  to  bacteria  is  an  open  question.  (See  fifth  edition  of  Hawk's 
Physiological  Chemistry,  pages  57  and  58.) 

Oxidases.  —  As  a  result  of  the  work  of  Dr.  C.  F.  MacDonald 
in  the  author's  laboratory,  the  following  conclusions  were 
reached  regarding  these  enzymes: 

First.  That  human  mixed  saliva  contains  an  oxidizing 
enzyme  distinct  from  ptyalin. 

Second.  That  the  enzyme  exhibits  the  properties  of  both 
an  oxydase  and  a  peroxydase. 

Third.  That  it  is  a  product  of  the  body  (probably  glandu- 
lar) metabolism  and  may  be  increased  in  quantity,  or  activity 
by  mastication. 

Fourth.  That  it  is  more  resistant  to  heat  than  ptyalin,  but 
more  easily  destroyed  by  acids. 

Fifth.  That  the  color  obtained  with  a  freshly  prepared  1% 
solution  of  pyrocatechol  is  -sufficient  test  for  this  enz>Tne  in 
saKva. 

The  test  for  oxidizing  enzymes  may  be  made  with  the  pyro- 
catechol as  given  on  page  314;  also  by  the  use  of  phenolphthaKn 


300  DIGESTION 

(reduced  phenolphthalein) .  This  last  reagent  has  recently  been 
rendered  available  by  the  work  of  Dr.  H.  L.  Amoss,  Harvard 
Medical  School,  who  has  given  us  a  concise  and  simple  method 
for  its  preparation.     (Jour.  Biolog.  Chem.,  191 2.) 

Phosphates  and  Carbonates.  —  These  salts  are  probably  pres- 
ent in  both  acid  and  neutral  forms;  that  is,  the  phosphate  may 
exist  as  Na2HP04  also  as  NaH2P04,  and  at  times  both  of  these 
may  be  present  at  once.  The  acid  carbonate,  NaHCOa,  is  an 
undoubted  constituent,  while  the  neutral  carbonate  is  probably 
not  present  at  all.  Chittenden  says  that  mixed  human  saliva 
contains  normally  no  sodium  carbonate  whatever. 

As  explained  by  Dr.  Kirk,  the  normal  reaction  by  which 
overacidity  of  the  blood  is  taken  care  of  by  renal  epitheHum 
is  H2CO3  +  Na2HP04  =  NaH2P04  +  NaHCOa,  and  when  con- 
ditions are  such  as  to  produce  larger  quantities  of  carbonic  acid 
than  the  kidneys  can  eliminate  in  accordance  with  the  above 
reaction,  there  is  an  increased  acidity  of  the  saliva  as  well  as  of 
the  urine.*  In  the  hypoacid  individual,  the  so-called  alkaline 
sodium  phosphate,  Na2HP04,  is  present  in  the  greater  quantity. 
In  diabetic  patients,  sugar  has  very  rarely  been  found  in  the 
sahva;  one  case  coming  under  the  observation  of  the  author 
was  that  of  a  woman  of  middle  age,  with  diabetes  of  long  stand- 
ing, with  8%  of  sugar  in  the  urine,  and  from  this  case  there  were 
obtained  a  very  few  osazone  crystals  by  subjecting  a  consider- 
able quantity  of  saliva,  after  concentration,  to  the  phenyl- 
hydrazine  test. 

Urea  has  been  repeatedly  found  in  the  saliva  of  patients 
suffering  from  chronic  nephritis. 

Acetone  is  of  quite  frequent  occurrence  in  the  saliva.  In 
diabetic  patients  this  substance  is  often  present  in  compara- 
tively large  amounts,  sometimes  sufficient  for  the  detection  of 
the  acetone  by  its  characteristic  odor.  Acetone  may  appear  in 
the  saliva  when  it  is  not  present  in  the  urine.     In  such  cases  it 

*  International  Dental  Journal,  February,  1904. 


SALIVA   PROPERTIES  AND  CONSTITUENTS  301 

has  usually  resulted  from  disordered  digestion  and  a  consequent 
faulty  metabolism.  (For  further  consideration  of  acetone,  see 
Urine.) 

Cholesterin  and  lecithin  have  been  found  by  Professor 
Michaels  in  pathological  saliva,  and  leucin  has  been  found  by 
IVIichaels  in  a  case  of  lupus  and,  according  to  Novey,  in  a  case 
of  hysteria. 

Of  the  crystaUine  salts  which  may  be  separated  by  evapora- 
tion of  dialyzed  saliva,  the  sodium  oxalate  and  the  lactates  and 
acid  lactates  of  lime  and  magnesia  are  of  the  most  importance 
and  have  been  the  most  thoroughly  studied.  As  these  salts 
may  likewise  be  separated  from  urine  their  significance  will 
be  studied  under  that  head. 

Ammonium  Salts.  —  Ammonium  salts  occur  chiefly  as  chlo- 
ride, probably  to  some  extent  as  sulphocyanate,  and  occasion- 
ally as  oxalate.  Professor  Michaels  says  that  ammonia  must 
be  considered  as  a  more  completely  oxidized  form  of  nitrogen 
than  urea;  hence  its  relative  increase  is  observed  in  all  diseases 
which  occasion  an  excess  of  nitrogen  and  urea,  as  in  tubercu- 
losis and  all  hypoacid  diatheses.  There  is  a  decrease  of  am- 
monia whenever  the  nitrogen  fails  to  reach  the  stage  of  oxidation 
represented  by  urea.  This  condition  is  accompanied  by  uric 
acid  and  other  products  of  deficient  oxidation,  and  characterizes 
the  hyperacid  state. 

While  these  statements  are  consistent  with  Dr.  Michaels' 
conception  of  the  hyper-  and  hypo-acid  diatheses,  the  student 
is  not  to  understand  that  ammonia  is  really  an  oxidation  prod- 
uct, for  we  have  already  seen  that  it  is  formed  by  the  splitting 
of  protein  derivatives.  Characteristic  crystals  of  ammonium 
chloride  may  be  found  by  microscopical  examination  of  the 
residue  obtained  by  evaporating  a  clear  drop  of  almost  any 
saliva.     (Plate  VIII,  Fig.  i,  page  316.) 

Potassium  Thiocyanate  represents  the  salts  of  HCNS  found 
in  saliva.     It  occurs  only  in  very  sHght  traces  in  other  body 


302  DIGESTION 

fluids,  and  in  saliva  only  to  the  extent  of  o.ooi  to  0.02%.  Dr. 
Michaels  considered  the  proportion  of  thiocyanates  relative  to 
the  ammonia  to  be  of  importance  and  states  that  in  health  the 
ammonium  salts  and  the  thiocyanates  are  present  in  very 
slight  amounts,  and  the  color-tests,  with  Nessler's  solution 
and  with  ferric  chloride,  respectively,  are  of  about  equal  in- 
tensity. In  the  hyperacid  state  the  sulphocyanates  are  in 
excess  of  ammonia,  while  in  h^poacid  conditions,  the  anmionia 
exists  in  the  greater  quantity.  Sulphocyanate  is  detected  by 
means  of  ferric  chloride,  and  distinguished  from  meconates  and 
acetates,  as  indicated  by  Exp.  247,  page  417. 

As  we  shall  see  in  a  subsequent  chapter  the  intensity  of  color 
produced  by  ferric  chloride  and  thiocyanate  is  not  necessarily 
an  index  of  the  quantity  of  HCNS  present,  hence  the  above 
conclusions  are  of  questionable  value. 

The  sulphocyanates  are  normal  constituents  of  sahva,  and 
consequently  always  present.  According  to  A.  Mayer  (Deutsch. 
arch.  f.  khn.  med.,  Vol.  79,  No.  394),  the  sulphocyanates,  with- 
out doubt,  result  from  the  decomposition  of  proteins,  and  exist 
in  the  urine  in  quantities  variously  estimated  from  twenty  to 
eighty  milligrams  per  lit&r,  while  in  sahva  it  has  been  estimated 
from  sixty  to  one  hundred  milligrams  per  liter.  Professor 
Ludholz  of  the  University  of  Pennsylvania  says  that  the  sulpho- 
cyanates are  eHminated  in  increased  amounts  in  conditions 
where  there  is  a  lack  of  oxygen  in  the  system,  thus  corrobo- 
rating statements  of  Professor  Michaels  (see  Ammonia).  Dr. 
Fenwick  (Lancet,  1877,  Vol.  II,  page  303)  demonstrated  that 
the  quantity  of  KCNS  was  directly  dependent  upon  the  bile 
salts  in  the  biood.  He  found  an  increase  of  the  salt  in  liver 
disorders  attended  with  increase  of  bile  salts  in  the  blood,  and 
marked  increase  in  jaundice.  In  gout,  rheumatism,  and  con- 
ditions producing  pyorrhea,  it  is  also  claimed  to  be  present  in 
considerable  quantity. 

The  sulphocyanates  are  usually  present  in  more  than  normal 


SALIVA    PROPERTIES  AND  CONSTITUENTS  303 

quantity  in  the  saliva  of  people  addicted  to  smoking  tobacco.* 
The  claim  has  been  made  for  this  salt  that  it  exerts  a  specific 
antiseptic  action  toward  bacteria. 

While  the  sulphocyanates,  or,  in  fact,  any  salt  in  sufficient 
concentration,  will  have  an  inhibitory  action  on  the  growth  of 
bacteria,  it  is  rather  doubtful  if  this  is  the  particular  office  of 
KCyS  in  the  saliva. 

Nitrites.  —  That  nitrites  exist  in  most  salivas  is  without  ques- 
tion. So  far  as  we  know  at  present,  the  nitrites  are  apparently 
incidental,  and  occur  as  intermediate  products  in  the  oxidation 
of  am_monia  to  nitrates,  just  as  they  do  otherwise  in  nature  out- 
side of  the  animal  body. 

It  is  not  at  all  improbable  that  the  proportion  of  nitrates  is 
dependent  upon  activities  of  the  oxidases.  This  has,  in  some 
cases  at  least,  been  proven  to  be  the  case,  as  the  same  sample 
of  sahva  has  frequently  given  steadily  diminishing  quantities 
of  nitrites  until  they  have  wholly  disappeared  in  cases  contain- 
ing active  oxidizing  enzymes. 

Nitrates  occur  in  the  sahva  but  so  far  as  known  are  without 
clinical  significance. 

*  See  article  by  Dr.  J.  Morgan  Howe  in  Jour,  of  the  Allied  Societies,  Vol.  4, 
p.  183. 


CHAPTER  XXXIV. 
ANALYSIS    OF   SALIVA. 

The  analysis  of  saliva  may  be  taken  up  from  two  distinct 
standpoints,  and  considering  our  present  lack  of  positive  knowl- 
edge on  this  subject  it  may  for  a  while  be  expedient  so  to  study 
it.  First,  we  will  study  a  few  tests  of  saliva  of  such  a  character 
that  they  may  be  made  with  simple  apparatus,  and  which  might 
be  used  by  any  dental  practitioner  with  sufficient  time  and 
interest,  to  contribute  to  our  general  knowledge;  secondly, 
we  may  study  saUva  by  accurate  laboratory  methods  which 
are  not  available  for  general  use,  but  which  are  necessary  for 
the  estabhshment  of  positive  data,  and  in  fact  necessary  for  an 
intelligent  schedule  of  tests  under  division  one. 

In  191 1  and  for  one  or  two  years  previous  the  National 
Association  made  an  effort  to  establish  uniform  methods  of 
salivary  analysis,  and  it  is  deeply  to  be  regretted  that  this 
effort  was  not  continued  until  a  system  of  examination  had 
been  perfected  which  might  have  become  a  recognized  one  for 
all  workers  along  these  lines.  A  necessity  of  uniform  methods 
is  generally  recognized  by  other  classes  of  chemists  but  as  yet 
the  fact  remains  that  the  dental  chemist  is  obliged  to  formulate 
his  own  analytical  schemes. 

We  shall  make  three  divisions  of  the  methods  to  be  used. 
Methods  marked  I  are  in  part  taken  from  Professor  Michaels 
and  are  the  simplest  ones  applicable  to  small  amounts.  They 
will  give  results  of  varying  degrees  of  accuracy,  but  are  of  value 
because  of  the  ease  and  rapidity  with  which  they  may  be  used. 

Methods  marked  II  are  retained  from  Dr.  Ferris'  report  to 
the  National  Dental  Association  at  its  annual  meeting  in  191 1, 

304 


ANALYSIS  OF  SALIVA  305 

and  reported  in  the  Dental  Cosmos  for  November  of  that  same 
year,  on  pages  1295,  etc. 

Methods  marked  III  are  those  which  the  author  believes  to 
be  the  most  accurate  and  the  most  satisfactory  in  exhaustive 
determinations. 

Physical  properties  of  the  saliva  should  first  be  noted.  In 
method  I,  the  color  and  appearance  of  the  perfectly  fresh  sample 
is  to  be  carefully  compared  with  the  appearance  and  color  after 
standing  for  forty-eight  hours  in  a  small,  tightly  covered  vial. 
The  color  may  be  yellowish,  greenish,  or  brown,  according  to 
the  variety  of  the  derivative  of  bihverdin  from  which  the  color 
is  obtained.*  The  general  appearance  may  also  change  inde- 
pendently of  any  color.  A  saliva  that  is,  when  fresh,  hypoacid 
in  character,  is,  after  forty-eight  hours,  usually  markedly  opal- 
escent and  of  offensive  odor,  while  a  hyperacid  saliva  may  have 
become  clear  or  cloudy  but  without  odor. 

By  method  II,  we  should  add  to  this  examination  a  viscosity 
test  which  will  be  of  value  as  indicating  the  amount  of  mucin,  as 
probably  the  mucin  content  affects  the  viscosity  more  than  any 
one  constituent. 

The  viscosity  may  be  determined  by  use  of  the  apparatus 
pictured  in  Fig.  21  (page  306).  '       . 

The  essential  features  of  the  viscosimeter  are  a  straight 
graduated  tube  with  the  constriction  (C)  jacketed  so  that  the 
conditions  under  which  a  given  sample  will  pass  through  the 
opening  will  always  be  under  absolute  control. 

The  apparatus  is  standardized  by  partly  filling  with  dis- 
tilled water  in  which  the  bulb  of  a  thermometer  is  immersed. 

The  temperature  of  the  distilled  water  is  brought  to  25°  C. 
The  thermometer  is  removed  to  facilitate  reading  and  from 
5  to  10  c.c.  of  the^Hquid  are  allowed  to  run  out,  the  time  con- 
sumed being  accurately  determined  by  a  stop  watch. 

*  Dr.  Joseph  P.  Michaels.  S.  S.  White's  reprint  of  paper  read  before  Inter- 
national Dental  Congress,  Paris,  1900. 


3o6 


DIGESTION 


Fig.  21. 


ANALYSIS  OF  SALIVA 


307 


The  viscosity  of  saliva  is  determined  in  the  same  way,  care 
being  taken  that  only  a  perfectly  clear  solution  is  used  as  j&ne 
particles  will  clog  the  opening  at  C.  The  use  of  the  stop  cork 
as  pictured  in  Fig.  21  is  undesirable,  in  fact  it  has  been  found 
that  straining  the  sahva,  filtering  through  paper  or  even  cen- 
trifugahzing  in  order  to  separate  the  soHd  portions  will  occasion 
a  variation  in  the  results  obtained.  The  first  determination 
should  be  carefully  made  and  used,  as  repeated  determinations 
result  in  a  regular  diminution  of  the  viscosity  figure  due  to 
mechanical  changes  brought  about  by  passing  the  saHva  through 
the  very  small  opening  at  C. 

If  the  constriction  of  the  graduated  tube  is  sufficiently  great, 
i.e.,  the  opening  sufficiently  small,  comparison  may  be  made 
by  counting  drops  dehvered  in  a  given  time.  This  is  not  ad- 
vised, as  there  is  much  greater  difficulty  in 
obtaining  the  saHva  free  enough  from  sus- 
pended particles  so  as  not  to  clog  the  tube. 

The  inner  tube  should  always  be  filled 
to  the  same  mark  in  the  determination  as 
that  used  in  the  standardization  of  the 
instrument. 

The  reaction  may  be  taken  in  method  I 
by  the  simple  use  of  litmus  paper.  This 
test  has  a  general  value,  and  is  sufficient  to 
detect  extreme  conditions.  Our  second 
method  should  be  a  quantitative  one,  and 
the  degree  of  alkahnity  should  be  deter- 
mined by  indirect  titration.  Add  excess 
of  N/ioo  HCl  to  10  c.c.  of  sample,  and  ti- 
trate back  to  yellow  color  with  N/ioo 
NH4OH.  Use  paranitrophenol  as  indicator 
ity,  using  N/ioo  alkali  and  neutral  phenolphthalein  as  an  indi- 
cator, should  be  determined  next.  Then  the  reaction,  after 
driving  off  carbon  dioxide,  should  be  ascertained.    The  per- 


FiG.  2  2.  —  Pykxiometer. 


The  degree  of  acid- 


3o8 


DIGESTION 


Fig.  23. 


manent  acidity,  if  such  exists,  should  be  found  a  useful  factor 

in  the  study  of  Dental  Caries  and  may  be  determined  by  the 

apparatus  pictured  on  page  294. 

Specific  Gravity  may  be  taken  (Method  I)  by  an  ordinary 

urinometer  or  a  specific  gravity  bulb 
if  the  quantity  is  sufficient,  the  read- 
ing to  be  made  from  beneath  the  sur- 
face of  the  Hquid.  If  the  quantity  of 
the  saliva  is  small,  it  may  be  diluted 
with  an  equal  volume  of  water,  and 
the  last  two  figures  multiplied  by  two 
will  give  the  gravity  of  the  undiluted 
sample,  or  the  gravity  may  be  taken 

by  the  pyknometer  in  which  the  bulb  of  the  instrument  is  filled 

with  saliva  accurately  to  the  mark  M  (Fig.  22),  and  then  the 

reading  of  course  on  this  instrument  will 

be  from  the  bottom  up,  and  the  lower  the 

bulb  sinks  the  greater  will  be  the  gravity 

of  the  sample.     This  method,  devised  by 

S.  A.  De  Santos  Saxe,  M.  D.,  for  use  in 

examination  of  urine,  has  been  suggested 

by  Dr.  Ferris  and  adopted  by  the  National 

Dental  Association  as  an  official  method. 
For  very  accurate  work  the  use  of  spe- 
cific gravity  bottles  is  recommended.    These 

may  be   obtained  holding  one,   two,   and 

five  cubic  centimeters  (Fig.  23),  and  with 

an  accurate  balance  of  course  the  gravity 

can  be  accurately  obtained. 
Thiocyanate    (Sulphocyanate)    Tests.  — 

(Method  I.)     To  a   large  drop  of  saliva 

on  a  white   porcelain  surface,  add  about 

half  as  much  5%  ferric  chloride,   acidified  with  hydrochloric 

acid.    A  reddish  coloration  indicates  the  presence  of  thiocya- 


A  B 

Fig.  24.  —  Sulphocyanate 
Tubes. 


ANALYSIS  OF  SALIVA  309 

nate.  "(Method  II.)  Use  a  colorimetric  scale  (Ferris  and 
Schradieck),  place  i  c.c.  of  the  specimen  in  tube  A;  i  c.c.  of 
1/2000  ammonia  sulphocyanate  in  tube  B  (Fig.  24);  add  two 
drops  of  a  5%  ferric  chloride  solution  to  each  tube,  add  aqua 
distillata  in  tube  B,  until  its  color  matches  that  of  the  specimen. 
Read  the  scale  in  thousandths  and  ten  thousandths. 

"  Care  must  be  taken  to  have  the  bottom  of  the  meniscus 
on  the  Kne.  If  these  tubes  are  introduced  in  the  color- 
imeter, the  readings  can  be  made  more  accurately.  If,  later, 
diacetic  acid  ester  or  other  substances  giving  similar  color 
with  ferric  chloride  are  found,  a  correction  is  made  in  the  find- 
ing." 

With  an  excess  of  ferric  chloride  this  test  gives  an  idea  of 
whether  the  amount  of  thiocyanate  is  much  or  little,  but  the 
careful  dilution  of  a  sample  and  comparison  with  standard  has 
been  found  to  be  practically  valueless  for  small  amounts,  which 
fact  may  be  explained  by  the  following  experiment. 

If  ferric  chloride  and  potassium  thiocyanate  are  mixed  in 
molar  proportions  and  diluted  one  to  one  thousand  with  dis- 
tilled water  a  solution  results  which  is  within  the  lower  limits 
of  the  thiocyanate  content  of  the  saliva,  but  it  also  happens 
that  ferric  thiocyanate  of  this  strength  dissociates  so  that  10  c.c. 
in  a  25  c.c.  cylinder  wiU  have  only  a  very  pale  straw  color  (the 
undissociated  Fe(CNS)3  only  is  red). 

If  a  drop  of  FeCls  solution  (M/i)  is  added  the  reddish  color 
is  restored,  the  ferric  chloride  being  in  excess,  but  the  addition 
of  5  c.c.  of  saliva  containing  the  average  amount  of  thiocyanate 
instead  of  increasing  the  color  on  account  of  the  additional 
Fe(CNS)3  produced,  causes  the  color  to  become  much  paler 
than  if  5  c.c.  of  distilled  water  had  been  added.  The  explana- 
tion is  obvious.  The  total  amount  of  ferric  thiocyanate  pro- 
duced, while  still  within  the  Hmits  of  the  salivary  content,  is 
not  concentrated  enough  but  what  the  proportion  of  ionized 
salt  is  still  in  excess,  and  further  the  added  saliva  has  con- 


3IO 


DIGESTION 


tributed  a  certain  amount  of  KCl  which  will  reduce  the  color 
by  inducing  the  reverse  reaction. 

3  KCl  +  Fe(CNS)3  =  FeCls  +  3  KCNS. 

Addition  of  either  the  acid  or  alkaline  sodium  phosphates 
(both  probable  constituents  of  saliva)  will  also  decrease  the 
intensity  of  the  color,  so  in  order  to  make  accurate 
comparisons  of  very  dilute  solutions  it  is  necessary  to 
know  the  amounts  of  ionizable  salts  in  the  sample, 
which  is  impracticable. 

Ammonium   Salts.  —  (Method  I.)     To  a  drop  of 
saliva  add  one  drop  of  Nessler's  reagent:    a  yellow 
to  brown  color  shows  the  presence  of  ammonium  salts. 
If  a  precipitate  forms  by  the  addition  of  Nessler's 
reagent,  it  indicates  either  a  large  amount  of  ammo- 
nia or  the  presence  of  urobilin.     If  due  to  urobilin 
the  precipitate  is  of  a  rose  color  after  desiccation. 
Ammonium  salts  are  usually  seen  in  the  evaporated 
drop  examined  by  polarized  light.    (Plate  VIII,  Fig.  i .) 
(Method  III.)     A  modification  of  Dr.  Folin's  am- 
monia test  in  urine,  using  the  Duboscq  colorimeter. 
Measure  out  10  c.c.  of  saliva  in  a  large  Jena  test- 
tube.     Add  2  c.c.  of  a  solution  containing  {a)  potas- 
sium oxalate,  (6)  potassium  carbonate  (15%  of  each). 
Fig.  25.      By  means  of  an  air  current,  drive  the  ammonia  through 
a  Folin  absorption-tubp  (Fig.  25)  into  a  100  c.c.  wide- 
mouth  bottle  containing  2  c.c.  N/io  HCl,  and  about  30  c.c.  water. 
In  twenty  minutes,  all  the  ammonia  should  have  gone  over. 

Remove  the  deHvery-tube,  rinsing  it  with  water,  and  transfer 
contents  of  bottle  to  100  c.c.  measuring  flask,  rinsing  with 
sufficient  water  to  make  total  volume  about  60  c.c. 

Pipette  out  i  c.c.  of  standard  ammonium  sulphate  into  an- 
other 100  c.c.  measuring  flask  and  dilute  with  water  to  about 
60  c.c. 


ANALYSIS  OF   SALIVA  3II 

Nesslerize  both  solutions  simultaneously  in  the  following 
manner.  Provide  two  small  beakers  (100  c.c.)  and  place  from 
10  to  15  c.c.  of  distilled  water  in  each.  Add  to  each  5  c.c.  of 
Nessler's  reagent.  Mix  the  reagent  with  water,  and  add  im- 
mediately to  the  ammonia  solutions.  Add  about  one-third  of 
the  diluted  Nessler  reagent  at  a  time,  and  shake  after  each 
addition. 

Fill  both  flasks  up  to  mark  with  distilled  water,  mix  and 
compare  the  colors  by  means  of  a  Duboscq  colorimeter  (Fig.  20, 
page  295). 

Urea.  —  Reagent,  sodium  hypobromite  as  used  for  urea  in 
urine  analysis  (Appendix,  page  427). 

Fill  the  tube  of  a  Ferris  modified  Doremus  ureometer  with  a 
saturated  salt  solution.  Close  the  stopper,  and  add  i  c.c.  of 
sahva  to  the  upper  tube.  Allow  this  to  run  through  the  stopper 
carefully,  then  close,  and  add  i  c.c.  of  the  reagent.  When  this 
has  gone  through,  close  the  stopper  quickly,  set  up  the  appa- 
ratus, and  allow  to  stand  one  hour  or  longer.  Then,  by  gently 
tapping,  cause  any  bubbles  adhering  to  the  sides  of  the  tube 
to  rise  to  the  top,  and  read  the  amount  of  gas  collected.  Each 
division  represents  0.025. 

Chlorides.  —  (Method  I.)  To  a  drop  of  saliva  add  a  small 
drop  of  a  5%  solution  of  neutral  chromate  of  potassium,  K2Cr04. 
Mix  with  a  glass  rod  and  add  one  drop  of  a  1/10%  solution  of 
silver  nitrate.  This  constitutes  the  test  for  chlorine,  which, 
if  present  in  normal  quantities,  will  give  a  reddish  precipitate, 
gradually  becoming  w^hite.  Should  the  precipitate  remain  red 
it  shows  the  chlorine  deficient  or  less  than  normal  in  amount. 
If  the  precipitate  rapidly  turns  white,  or  if  a  white  precipitate 
is  formed  to  the  exclusion  of  the  red,  chlorine  is  increased  in 
amount.     High  chlorine  is  indicative  of  h}^oacid  diathesis. 

(Method  II.)  To  i  c.c.  of  the  specimen  add  4  c.c.  of  distilled 
water  and  two  or  three  drops  of  potassium  chromate;  then 
titrate  with  N/40  silver  nitrate  solution,  until  the  first  appear- 


312  DIGESTION 

ance  of  a  permanent  reddish  tinge.  Multiply  the  number  of 
cubic  centimeters  of  nitrate  used  by  0.0886  to  find  the  amount 
of  chlorine  in  100  c.c.  of  saliva. 

(Method  III.)  Proceed  as  in  Method  II  except  that  it  is 
recommended  to  use  5  c.c.  of  the  specimen  and  N/20  silver 
nitrate  solution.  Then  the  number  of  cubic  centimeters  of 
silver  solution  used  multiplied  by  0.00177  will  give  the  weight 
of  chlorine  in  the  5  c.c.  of  saliva  taken.  This  times  twenty 
will  give  the  amount  in  100  c.c.  or  the  per  cent. 

Glycogen.  —  (Method  I.)  A  drop  of  sahva  may  be  tested 
for  glycogen  by  the  addition  of  one  drop  of  an  aqueous  solution 
of  iodine  and  potassium  iodide.  This  must  be  left  for  some 
time,  as  the  test  is  not  obtained  until  the  drop  is  dried;  then, 
if  the  color  is  a  feeble  violet  around  the  edge,  glycogen  is  indi- 
cated. If  the  color  is  a  strong  brown-red  it  indicates  erythro- 
dexterin,  if  gray  or  black  a  reducing  sugar. 

Phosphates.  —  The  phosphates  in  saliva  are  determined  as 
in  urine  except  that  it  is  necessary  to  modify  the  process  sUghtly 
as  given  on  page  340. 

Calcium  may  be  determined  by  the  following  volumetric 
method  recommended  by  Dr.  Percy  R.  Howe,  Dental  Cosmos, 
April,  191 2.  To  5  c.c.  of  saUva,  add  as  much  more  distilled 
water  and  a  shght  excess  of  oxalic  acid  or  ammonium  oxalate 
(5  c.c.  of  normal  solution  will  be  sufhcient).  Add  ammonium 
water  to  alkaline  reaction,  heat  nearly  to  the  boihng-point, 
and  allow  to  stand  for  20  to  30  minutes.  Filter  through  a 
hardened  filter  paper  into  a  small  beaker  which  is  allowed  to 
stand  on  a  piece  of  black  glazed  paper.  Under  these  circum- 
stances, a  shght  rotary  motion  of  the  beaker  will  show  if  any 
of  the  white  precipitate  of  calcium  oxalate  is  passing  through 
the  paper. 

After  filtration  is  complete,  wash  five  times  in  hot  distilled 
water;  then  place  the  precipitate,  together  with  the  paper,  into 
a  small  beaker,  add  about  30  c.c.  of  dilute  sulphuric  acid,  and 


ANALYSIS  OF  SALIVA 


313 


heat  nearly  to  the  boiling-point;    then  titrate  with  N/20  per- 
manganate solution. 

Acetone.  —  (Methods  I  and  III.)  In  the  fifth  drop  dissolve 
a  small  crystal  of  potassium  carbonate,  then  add  a  drop  of 
Gram's  reagent,  when  a  marked  odor  of  iodoform  will  indicate 
the  presence  of  acetone.  Should  this  odor  be  obtained,  it  is 
better  to  repeat  this  test  upon  a  microscope  slide,  and  examine 
carefully  for  the  characteristic  hexagonal  crystals  of  iodoform 
(Plate  V,  Fig.  i,  page  204). 

Nitrites.  —  (Method  I.)  Nitrites  may  be  detected  by  add- 
ing to  a  large  drop  of  saliva  on  porcelain  a  few  drops  of  freshly 
prepared  reagent,  made  by  dissolving  a  very  little  naphthyl- 
amine  chloride  and  an  equal  amount  of  sulphanilic  acid  in 
distilled  water  strongly  acidulated  with  acetic  acid.  A  purple 
coloration  is  a  test  for  nitrates. 

This  method  could  be  made  quantitative  in  a  manner  simi- 
lar to  the  colorimetric  methods  for  ammonia,  or  thiocyanate 
of  potassium;  but,  at  the  time  of  the  present  writing,  there 
seems  to  be  no.  particular  reason  for  this  amount  of  work. 

Amylolytic  Enzymes.  —  (Method  II.)*  Preparation  of  starch 
paste.  Put  15  c.c.  of  distilled  water  to  boil.  Meanwhile,  weigh 
out  three  grams  sterile  starch  and  mix  with  6  c.c.  cold  distilled 
water.  Add  drop  by  drop  under  constant  stirring  to  the  boihng 
water,  then  rinse  out  with  5  c.c.  of  distilled  water  any  particles 
of  starch  adhering  to  the  dish  and  add  to  the  boihng  starch 
solution.  Boil  one  minute  under  constant  stirring.  Cool  to 
blood  temperature  and  add  gradually  4  c.c.  of  N/ioo  iodine 
solution. 

This  makes  30  c.c.  of  a  10%  starch  solution,  which,  when 
colored,  is  of  a  dark  blue,  and  can  be  kept  several  days  in  the 
ice-box.    - 

Filling  the  Tubes.  —  Suck  up  the  paste  into  glass  tubes  of 
1.5  mm.  diameter,  and  cool  in  the  ice-box.     Just  before  using, 
*  Method  II  as  usual  by  Dr.  Ferris  (see  page  304). 


314  DIGESTION 

make  a  file  mark  i  cm.  from  the  end  of  the  tube  and  break  off 
the  piece  of  tubing  so  that  it  is  full  of  the  blue  starch  paste. 
Be  sure  that  this  small  tube  is  broken  so  as  to  leave  each  end 
square  and  full  of  paste.     Examine  under  low-power  microscope. 

Determination  of  Enzyme.  —  Immediately  after  delivery  of 
the  specimen,  measure  2  c.c.  of  saliva  into  a  test-tube.  Place 
it  in  the  small  tube  of  starch  paste,  and  heat  the  whole  in  a 
thermostat  at  from  37°  to  38°  C.  for  half  an  hour.  The  enzyme 
of  the  saliva  will  dissolve  the  paste  from  the  ends  of  the  tube, 
leaving  a  blue  column  of  paste  unchanged  in  the  center  of  the 
glass  tube.  After  half  an  hour,  measure  with  a  micrometer 
gauge  the  total  length  of  the  tube  and  the  length  of  the  blue 
starch  paste  column  remaining  undissolved.  The  difference 
between  these  two  measurements  represents  the  amount  of 
starch  digested  by  the  enzyme.  Since  the  quantity  of  ferment 
in  any  fluid  varies  with  the  square  of  the  length  of  the  column 
digested,  the  quantity  of  ferment  in  the  saliva  is  found  by 
squaring  this  difference.  Multiply  by  100  to  give  the  enzymic 
index. 

Oxidizing  Enzyme.  —  (Oxydase.)  Methods  I  and  III  con- 
sist of  treating  5  c.c.  of  saHva,  diluted  with  an  equal  volume  of 
water,  with  about  i  c.c.  of  a  1%  solution  of  pyrocatechol.  The 
color  obtained  is  a  characteristic  brown,  developing  within 
thirty  minutes. 

Mucin  and  Albumin.  —  (Method  I.)  Mucin  may  be  sepa- 
rated after  taking  the  gravity  by  the  addition  of  a  little  acetic 
acid.  It  should  then  be  filtered  off,  but  it  will  be  necessary  to 
dilute  and  agitate,  in  order  that  a  fairly  clear  filtrate  may  be 
obtained. 

Albumin  may  be  demonstrated  in  the  filtrate,  from  which 
mucin  has  been  separated  by  underlaying  with  strong  nitric 
acid.  This  is  Heller's  test  for  albumin  in  the  urine,  and  is  best 
performed  in  a  small  wine-glass  with  round  bottom  and  plain 
sides. 


ANALYSIS  OF  SALIVA  315 

Total  Solids  and  Ash.  —  (Method  II.)  These  should  be  de- 
termined immediately  upon  the  arrival  of  the  specimen  to  avoid 
error  through  evaporation  of  moisture. 

Use  a  platinum  or  fused  silica  dish  of  constant  weight  which 
has  been  kept  in  a  desiccator  over  sulphuric  acid.  Weigh  the 
dish  accurately  and  rapidly,  then  introduce  2I  c.c.  of  the  well- 
mixed  specimen  and  heat  in  a  drying  oven,  not  over  100  C, 
for  two  hours.  Then  place  in  the  desiccator  over  sulphuric  acid 
for  twelve  hours  or  longer,  and  weigh  accurately  and  rapidly. 

The  difference  between  these  weights  represents  the  weight 
of  total  solids.  To  calculate  the  percentage,  divide  by  two  and 
one-half  times  the  specific  gravity. 

Add  to  the  dish  two  or  three  drops  of  fuming  nitric  acid, 
and  heat  over  a  flame,  keeping  the  dish  two  inches  above  the 
top  of  the  flame,  until  the  black  color  has  become  white.  Heat 
in  the  direct  flame  until  glowing,  place  at  once  in  desiccator  to 
cool  for  one  or  more  hours,  and  weigh.  Calculate  the  percent- 
age of  ash  in  same  manner  as  of  total  solids. 

(Method  III.)  Total  soHds  and  ash  are  best  obtained  as 
follows:  evaporate  over  a  water  bath  five  grams  of  the  sample 
thoroughly  mLxed  with  a  weighed  amount  (half  a  gram)  of 
ignited  magnesium  oxide.  The  weight  of  residue  (less  the 
magnesia)  obtained  by  drying  at  100°  C,  gives  the  total  solids. 
These  may  be  ignited  until  white  ash  is  obtained  and  again 
weighed.     The  second  weight  (less  magnesia)  gives  the  ash. 

The  use  of  the  magnesium  oxide  serves  to  retain  carbonates 
and  chlorides  in  the  total  solids  and  the  chlorides  in  the  ash. 
It  also  obviates  the  necessity  of  oxidation  with  nitric  acid,  which 
would  decompose  many  of  the  inorganic  constituents  of  the  ash. 

To  determine  weight  of  sediment  obtain  total  solids  as 
above ;  then  if  a^  portion  of  the  saKva  is  carefully  filtered  and 
the  soKds  determined  in  the  clear  filtrate  by  the  same  method, 
the  dift'erence  between  the  two  determinations  of  solids  will  be 
the  weight  of  sediment,  epithelium,  leucocytes,  etc. 


3i6 


DIGESTION 


Crystals  from  the  Dialyzed  Saliva. 

To  obtain  characteristic  crystals,  as  has  been  explained  in 
considering  the  subject  of  micro-chemistry,  uniformity  as  to 
conditions  under  which  the  crystallization  takes  place  is  a 
necessity.     In  the  case  of  saliva,  however,  we  are  not  producing 

new  compounds,  but  simply  search- 
ing for  compounds  already  formed 
and  existing  in  unknown  proportions 
in  the  samples  tested.  It  is  therefore 
necessary  to  make  several  prepara- 
tions of  each  sample,  in  order  that 
we  may  obtain  the  widest  range  of 
possibility  for  characteristic  crystal- 
Hzations.  The  following  method  of 
procedure  will  usually  give  satisfac- 
tory results:  For  a  dialyzer  use  a 
fairly  wide  glass  tube,  over  one  end 
of  which  has  been  tightly  tied  a  piece 
of  parchment  (Fig.  26),  or,  better,  a  small  dialyzing  tube 
made  entirely  of  parchment.  Place  about  15  c.c.  of  saHva 
in  the  dialyzing  tube,  and  suspend  it  in  a  small  beaker 
or  wine-glass  which  contains  an  equal  volume  of  distilled 
water.  At  the  end  of  twenty-four  hours  the  distilled  water 
will  contain  the  dialyzable  salts  in  nearly  the  same  con- 
centration as  existed  in  the  original  saliva.  Take  four  previ- 
ously prepared  cell-shdes  (microscope  slides  on  which  a  ring  of 
Bell's  or  other  microscopical  cement  has  been  placed)  and  fill 
each  cell  full  of  the  dialyzed  saliva.  Put  number  one  in  a  warm 
place  that  it  may  evaporate  rapidly,  leave  number  two  exposed 
to  the  air  at  the  room  temperature  and  it  will  dry  in  from  half 
to  three-quarters  of  an  hour.  Place  number  tJrree  under  a 
large  beaker,  or  small  bell-jar,  and  cover  number  four  with  a 
cover-glass,  and  from  time  to  time  examine  the  crystals  that 


Fig.  26. 


PLATE   VIII.  — ANALYSIS   OF   SALIVA. 


Fig.  I. 
Ammonium  Chloride. 


Fig.  3. 
A,  Magnesium  Lactate  (P.  L.). 
B,  Calcium  Lactate  (P.  L.). 


Fig.  2. 
Sodium  Chloride,  |%. 


Fig.  4. 
A,  Magnesium  Acid  Lactate. 
B,  Calcium  Acid  Lactate. 


Fig.  5. 
Potassium  Chloride,  |%  Solution. 


Pig.  6. 
Potassium  Chloride,  |%  Solution. 


ANALYSIS  OF  SALIVA  ^       317 

may  be  formed.  Numbers  three  and  four  will  probably  take 
several  hours,  perhaps  several  days,  before  crystallization  is 
complete.  When  the  crystals  have  appeared,  the  preparation 
may  be  preserved  by  mounting  in  xylol  balsam.  In  attempt- 
ing to  obtain  crystals  from  the  saHva  before  dialyzation,  results 
are  usually  unsatisfactory,  owing  to  the  presence  of  mucin 
and  other  organic  substances  which  interfere  with  the  crystal- 
lization. The  crystals  obtained  by  this  method  are  principally 
sodium  oxalate,  lactates,  and  acid  lactates  of  lime  and  magnesia, 
and  rarely  urates  of  the  alkaHs.  (For  forms  of  these  crystals 
see  Plate  VIII,  Figs.  3  and  4,  and  Plate  II,  Fig.  4,  pages  316 
and  170.) 

Tests  for  Abnormal  Constituents. 

Acetone,  glycogen,  and  dextrin  have  already  been  considered. 
Urea  may  be  demonstrated  as  follows:  To  a  given  volume 
of  saliva  add  twice  as  much  alcohol.  This  serves  to  precipi- 
tate proteins.  Filter  and  evaporate  on  a  water-bath  till  original 
volume  is  reached,  or  evaporate  to  less  than  original  volume, 
and  make  up  with  distilled  water.  Then  determine  urea  by 
method  suggested  by  Dr.  Ferris  and  given  on  page  311. 

Lactic,  butyric,  and  acetic  acids  may  each  be  tested  for,  quah- 
tatively,  by  the  methods  given  under  gastric  digestion  (q.v.) . 

Mercury.  —  A  very  delicate  test  may  be  made  for  this  metal 
as  follows:  Collect  as  large  a  sample  of  saliva  as  possible,  dilute 
with  an  equal  volume  of  water,  acidify  with  a  few  drops  of 
hydrochloric  acid,  throw  in  a  few  very  small  pieces  of  copper- 
turnings,  which  have  been  recently  cleaned  in  dilute  nitric  acid, 
and  boil  for  at  least  one-half  hour,  keeping  up  the  volume  by 
occasional  additions  of  water.  Remove  the  copper-filings,  dry 
thoroughly  on-  filter-paper,  and  place  in  a  large-sized  watch- 
glass  (3  inches).  In  another  watch-glass  of  similar  size  place 
one  drop  of  solution  of  gold  chloride,  and  quickly  invert  so  that 
the  drop  remains  hanging  on  the  under  side  of  the  glass.     Now 


3l8  DIGESTION 

place  this  watch-glass  directly  over  the  one  containing  the 
copper,  so  that  the  chloride  of  gold  shall  be  suspended  directly 
above  the  turnings  and  perhaps  a  half  inch  from  them,  then 
gently  heat  the  lower  watch-glass  with  a  very  small  flame, 
when  the  slightest  trace  of  mercury,  which  may  have  been 
deposited  upon  the  copper,  will  be  volatilized,  reducing  the 
chloride  of  gold,  and  causing  a  purplish  ring  to  appear  around 
the  edge  of  the  drop.  If  no  reduction  of  the  gold  occurs,  mer- 
cury is  absent. 

Lead,  which  occasionally  occurs  in  sahva,  may  be  detected 
by  the  methods  given  under  urine. 

Microscopical  examination  of  the  sediment  should  be  made 
in  every  instance.  Normal  saliva  will  contain  epithelium  from 
various  parts  of  the  oral  cavity,  an  occasional  leucocyte,  and 
occasional  mold  fungi,  leptothrix,  etc.  Constituents,  which  per- 
haps are  not  properly  classed  as  normal  and  at  the  same  time 
are  not  pathological,  are  fat  globules,  a  rare  blood-corpuscle, 
sarcinae,  extraneous  material  as  food  particles,  starch  granules, 
muscle  fibers,  etc.  An  excessive  amount  of  blood,  fat,  pus,  or 
micro-organisms  would,  of  course,  indicate  pathogenic  con- 
ditions. The  bacteriological  investigation  of  samples  of  saliva 
is  always  of  interest,  and  may  be  necessary,  but  the  detailed 
methods  of  such  investigation  do  not  lie  within  the  scope  of 
this  work. 


CHAPTER  XXXV. 
GASTRIC   DIGESTION. 

Digestion  begins  with  the  action  of  the  saliva  upon  the 
carbohydrates,  and  if  mastication  is  sufficiently  prolonged,  the 
ptyalin  may  convert  an  appreciable  quantity  of  starchy  food 
into  a  more  soluble  form  before  it  reaches  the  stomach.  In  the 
stomach  the  amylolitic  action  of  the  saliva  is  stopped  by  the 
contact  with  the  gastric  juice.  A  certain  amount,  however,  of 
salivary  digestion  takes  place  within  the  stomach,  due  to  the 
fact  that  considerable  time  necessarily  elapses  before  the  acid 
of  the  gastric  juice  has  been  secreted  in  sufficient  quantity  to 
completely  permeate  and  acidify  the  mass  of  food  received 
from  the  esophagus.  As  has  been  previously  shown,  a  very 
feeble  degree  of  acidity  is  conducive  to  the  activity  of  the 
amylolytic  ferment.  The  average  alkalinity  of  the  saliva,  cal- 
culated as  Na2C03,  is  about  0.15  of  one  per  cent. 

The  first  step  in  the  gastric  digestion  is  probably  the  union 
of  the  stomach  hydrochloric  acid  with  the  proteins,  forming 
acid  albumins  (metaproteins)  or  allied  bodies  which  are  changed 
by  pepsin,  which  is  the  active  digestive  ferment  of  the  stomach, 
into  the  proteoses,  and  slight  amounts  of  the  various  peptones, 
following  practically  the  changes  produced  experimentally  on 
page  418. 

Pepsin  is  an  active  proteolytic  enzyme  occurring  in  the  cells 
of  the  stomach- wall  as  pepsinogen;  this  latter  is  decomposed  by 
the  hydrochloric  acid  with  the  formation  of  free  pepsin.  Pepsin 
works  only  in  faintly  acid  solutions,  and  in  the  stomach  carries 
the  digestion  of  proteins  but  little  beyond  the  stage  of  the 
proteoses. 

.319 


320  DIGESTION 

Hydrochloric  acid  is  obtained  from  the  fundus  glands  by  an 
interchange  of  radicals  between  alkaline  chlorides  and  the  car- 
bonates of  the  blood.*  The  quantity  present  varies  from 
nothing  to  0.3%,  the  degree  of  acidity  most  favorable  for  peptic 
activity  being  about  0.18%. 

Aside  from  HCl,  various  organic  acids  may  be  present  in 
the  stomach  contents;  lactic  acid,  butyric  acid,  and  acetic  acid 
are  the  most  important  of  this  class,  tests  for  which  are  referred 
to  under  analysis  of  gastric  contents,  page  417. 

Hydrochloric  acid  combines  with  protein  substances  of  the 
food,  forming  a  rather  unstable  compound  in  which  condition 
the  acid  is  known  as  combined  hydrochloric  acid  in  distinction 
from  the  free  hydrochloric  acid  which  the  gastric  juice  may  also 
contain.  The  combined  acid  possesses  only  in  modified  form 
the  properties  of  the  free  acid,  and  hence  is  less  liable  to  stop 
the  digestive  action  of  ptyalin  from  the  saliva. 

Rennin  is  a  second  enzyme  found  in  the  stomach.  This,  like 
pepsin,  also  exists  as  a  zymogen,  and  is  liberated  or  developed 
by  the  presence  of  acid.  Its  action  is  particularly  the  curdling 
of  milk,  i.e.,  the  decomposition  of  caseinogen  (Exp.  253),  and 
consequent  coagulation  of  the  casein. 

Tliis  process  involves  a  splitting  of  the  caseinogen  into  a 
slight  amount  of  a  peptone-Hke  body  and  soluble  casein.  From 
this  latter  substance  the  insoluble  curd  is  produced  by  the 
action  of  the  calcium  salts  contained  in  the  milk.  Gastric 
lipase,  or  stomach  steapsin,  a  fat-splitting  enzyme,  is  a  third 
enzyme,  existing  in  the  stomach  in  very  small  quantities,  the 
action  of  which  is  comparatively  weak  and  of  but  slight 
importance. 

It  is  to  be  noted  that  the  digestive  action  of  the  stomach 
is  only  partial,  the  proteins  being  split  into  proteoses  and  to 
some  extent  into  peptones,  while  further  action  is  left  for  the 
more  active  ferments  of  the  pancreatic  and  intestinal  juices. 

*  Long's  Physiological  Chemistry. 


CHAPTER  XXXVI. 
PANCREATIC   DIGESTION  AND  BILE. 

It  may  be  an  aid,  in  remembering  the  various  digestive  fer- 
ments, to  note  that  in  the  saKva  we  have  one  principal  ferment, 
ptyahn;  in  the  stomach  we  have  two,  pepsin  and  rennin;  in 
the  pancreatic  juice,  three,  trypsin,  amylopsin,  and  steapsin. 
In  addition  to  these  the  pancreatic  juice  contains  a  ferment 
similar  to  rennin  known  as  ch}Tiiosin. 

Trypsin  is  the  proteolytic  enz}TTLe  of  the  pancreatic  juice. 
It  is  a  much  more  energetic  digestive  agent  than  pepsin,  con- 
verting the  proteoses  into  peptones,  tyrosin,  leucin,  and  other 
amino  acids.  It  also  differs  from  pepsin  in  that  it  acts  in  an 
alkahne  medium  rather  than  an  acid.  Tr3^sin  exists,  Uke 
other  proteolytic  enzymes,  as  a  parent  enzyme,  trypsinogen, 
which  in  itself  is  not  a  digestive  ferment,  but  which  is  rendered 
active  (activated)  by  another  substance  known  as  enterokinase. 

The  enterokinase  occurs  in  the  intestinal  juice,  and  seems  to 
be  secreted  only  as  it  is  needed  for  the  activation  of  the  tryp- 
sinogen. Enterokinase  does  not  in  itself  possess  digestive 
power,  but  its  action  is  destroyed  by  heat  and  in  this  it  resembles 
the  enzymes. 

Amylopsin,  or  pancreatic  amylase,  is  the  starch-digesting 
enz}Tne  of  the  pancreatic  juice.  Here,  again,  we  have  an 
enzyme  much  more  energetic  in  its  action  upon  carbohydrates 
than  the  ptyahn  of  the  saHva.  It  converts  starch  into  maltose 
and  to  some  extent  to  dextrin.  The  amylopsin  is  active  in 
faintly  alkahne  or  very  faintly  acid  solution;  more  acid,  how- 
ever, retards  its  action. 

The  starch-sphtting   enzyme   of  the  pancreas  is  dependent 

321 


322  DIGESTION 

upon  the  presence  of  electrolytes;  if  these  are  removed  by 
dialysis  a  juice  results  which  is  devoid  of  starch-splitting  power. 
A  halogen  ion,  chlorine  or  bromine,  is  apparently  essential  to 
the  activity  of  this  enzyme.* 

Steapsin,  Kpase,  is  the  fat-splitting  enzyme  of  the  pancreatic 
juice,  inactive  until  it  comes  in  contact  with  constituents  of 
the  bile.  It  splits  the  fat,  as  indicated  on  page  266,  into  glycerol 
and  fatty  acids,  and  also  acts  as  an  emulsifying  agent.  The 
free  fatty  acids  thus  formed  unite  with  the  alkaline  bases  found 
in  the  intestines  to  form  soaps,  which  are  also  active  emulsifying 
agents. 

Chymosin,  or  pancreatic  rennin,  has  practically  the  same 
action  upon  caseinogen  as  the  gastric  rennin. 

The  pancreatic  juice  and  the  bile  enter  the  duodenum  in 
very  close  proximity,  and  the  digestive  action  of  each  is  depend- 
ent, to  a  considerable  extent,  upon  the  presence  of  the  other. 

Bile.  —  A  secretion  produced  by  the  liver  and  stored  in  the 
gall-bladder,  from  which  it  is  delivered  to  the  intestines,  where 
it  aids  materially  in  emulsification  and  absorption  of  the  fats. 

Composilion  of  Bile.  —  The  composition  of  bile  is  very  com- 
plex as  it  contains  a  portion  of  the  waste  products  of  metabo- 
lism as  well  as  substances  playing  an  important  part  in  digestion 
and  designed  to  be  reabsorbed  into  the  circulation. 

Among  the  first  class  are  the  two  principal  bile  pigments: 
the  bilirubin  (bile  red)  and  its  oxidation  product  bihverdin, 
(bile  green).  The  bile-pigments  are  derived  from  the  coloring 
matter  of  the  blood.  The  appearance  of  either  of  these  or  of 
their  derivatives,  in  either  urine  or  saliva,  is  indicative  of  patho- 
logical conditions  either  of  the  liver-  or  bile-ducts,  causing 
obstructions  to  the  outflow  of  the  bile  or  a  destruction  of  the 
red-blood    corpuscles. f     The    blood     pigments,    according    to 

*  Journal  of  the  American  Chemical  Society,  vol.  32,  p.  1087,  Kendall  and 
Sherman, 
t  Ogden. 


PANCREATIC  DIGESTION  AND  BILE  323 

Michaels,  are  easily  demonstrable  in  the  desiccated  saliva  by 
means  of  polarized  light. 

Cholesterol,  (C27H45OH?),  may  also  be  considered  a  waste 
product  of  the  bile.  It  is  excreted  with  the  feces;  when  re- 
tained it  is  likely  to  produce  "  gall  stones  "  which  are  often 
found  to  consist  of  fairly  pure  cholesterol  with  a  little  coloring 
matter. 

Cholesterol,  as  its  name  implies,  is  an  alcohol  containing  one 
hydroxyl  group  and  one  pair  of  double-bonded  carbon  atoms. 
It  is  soluble  in  hot  alcohol  from  which  it  may  be  crystallized 
as  thin,  colorless  plates.     (See  Plate  VII,  Fig.  4.) 

Two  important  acids  of  the  bile  are  taurocholic  and  glyco- 
cholic,  existing  principally  as  sodium  or  potassium  salts.  Gly- 
cocholic  acid  upon  hydrolysis  splits  into  a  simpler  acid  (cholic) 
and  glycocoU,  glycocoll  being  an  amino-acetic  acid  (page  225), 
which  is  undoubtedly -an  antecedent  of  urea. 

TaarochoKc  acid,  on  the  other  hand,  splits  into  cholic  acid 
and  taurine,  taurine  being  an  amino-ethyl  sulphonic  acid  (page 

252). 

The  Intestinal  Juice  contains  a  number  of  substances  play- 
ing an  important  part  in  the  preparation  of  food  material  for 
assimilation.  Among  them  is  erepsin  (erepase).  This  is  a 
protein-splitting  enz^Tue  acting  upon  the  products  of  tryptic 
digestion.  It  has  little  power  upon  the  simple  proteins,  but 
wdll  spht  the  peptones  into  amino  acids.  There  are  also  in  the 
intestinal  juice  certain  amylolytic  enzymes,  sucrase,  lactase,  and 
maltase  which  continue  the  digestive  action  started  by  amyl- 
opsin  or  by  ptyalin  of  the  saliva. 

The  intestinal  juice  contains  proteolytic  enzymes  which  will 
hydrolyze  the  nucleic  acids  left  undigested  by  other  enzymes 
of  the  stomach  and  pancreatic  juice.     (See  Exp.  261  page  421.) 

Secretin,  excreted  by  the  mucous  membrane  of  the  intestine, 
is  a  substance  differing  materially  from  the  digestive  ferments 
in  that  it  is  not  destroyed  by  heat.     It  acts  not  as  an  activator 


324  DIGESTION 

in  the  sense  that  it  starts  specific  chemical  action,  but  as  an 
essential  constituent  for  the  secretion  of  the  various  digestive 
fluids;  i.e.,  the  secretin  in  the  blood  starts  the  flow  of  pancre- 
atic juice,  for  instance,  which  contains  the  parent  enzyme, 
trypsinogen,  which  in  turn  requires  the  action  of  enterokinase 
before  it  is  in  condition  to  perform  its  work  of  digestion.  Some 
authorities  claim  that  the  secretin  itself  exists  as  a  pro-secretin, 
from  which  it  is  liberated  by  action  of  acid. 


PANCREATIC   DIGESTION  AND   BILE 


O^D 


•a 

u 

« 

a 

o 

iJ  c 

&0 

s, 

s 

0    CJ 

%a 

o 

u 

<->  n 

3 

3 

^•:p 

o 

U 

—   ra 

c 

5 

OO 

<--~— 

,       • 

o 

c  « 

o  5J 

a 

S 

o  g 

Zi    '- 

a 

C5 

^  o 

■3^ 
SO 

"3. 

a 

:j 

_o 

o 

o 

.2 

>.  >>   -H  ^ 

o 

— ?         cu      ^ 

< 

o 

S      8     > 

1-^  il 

>> 

8 

-M           -(->         o 

"o 

■i^ 

o              ■-  o 

E 

2      S    J 

S   E    .S-  S 

c. 

s 

S               o  S- 

< 

p.              flH          J 

Cli   <;      hJ    (X, 

J 

&, 

w                <J 

^ — . 

o 

0 

O           1 

i    .E     8 

l-g         ^ 

0"° 

_c 

-        3ci1 

^^         8 

S  S  o     .2  ^  S 

_w 

^^^^ 

E 

"1?  o  c^^-S  o 

'Z 

o  S  o|  o  C.2 

M  o 

0  5ig|c52 

^  o2   O'S   C   3 

o  c  w       S     e"" 

6 

J= 

Si3 

ISS     3  -Ij 

11 

_c 

9  "5  p  "o  ~^-z 

o 

•53 

S£g->.S  ^£ 

£§■■3     E   SS 

E 

_3  >  _3  -^  _5  >.  p 

sa 

a,    (Xf-a    w 

£a^S    H  c; 

H 

< 

O  —  O  C^  w  r"  y 

' — .^ — ' 

' — .^ — ^■— •■ — 

C         ,' 

j^ 

r^'o       d 

c 
c 

c 

o 

al                E 

*a 

a 

3 
1 

II 

It  il 
fill 

C-"        cS  "  C3 

1               1 

8    "oS     .S- 

o 

u  yi 

n       u  «  -(->     M 

>> 

_cS^-^ 

u       rt  ^  n!     v-a 

CU          C      fi, 

fii     U     Ph   c 

fe 

="' 

_c 

a 

'5 

_0  M 

„ 

C 

C3 

r!            o 

t3.S 

i 

C3        C3      C3  3 

1 

>> 

1      II 

.s  ^  1  s 

III 

1 

cSsb;      -g 

2 

^ 

'r-  <  M  £: 

<""' 

H 

-J3AUI      (^_: 

•• 

a 

"^ 

1«l 

> 

o 

5 

III 

i^  3-S 

■d 

>. 

a 

a 

o 
a 

c 

J3 

> 

I, 

"i 

x 

c 

> 

ca 

- 

a: 

'-- 

O, 

— 

■^ 

- 

_ 

^ 

C 

£ 

.2 

^ 

3 

o 

J2 

? 

■a 

'-3 

o 

3 

o 

o 

J 

^O 

■r. 

3 

c 

c 

C) 

^ 

s 

3 

o 

T) 

^ 

!^ 

p 

c 

u 

c 

c 

CJ 

H 

a 

fr. 

m 

PART   VI 1 1. 

URINE. 

CHAPTER  XXXVII. 

PHYSICAL    PROPERTIES    OF    URINE. 

Urine  is  a  solution  of  waste  products  from  the  blood.  It 
contains,  normally,  certain  coloring  matter,  urea,  uric  acid  in 
combination  with  alkaUne  bases,  various  organic  constituents 
in  shght  amounts,  including,  perhaps,  albumin  and  sugar, 
chloride  of  sodium,  sulphates  and  phosphates  of  the  alkahs  and 
the  alkahne  earths.  Abnonnally  the  urine  may  contain  albu- 
min, sugar,  uric  acid  as  such,  bile,  salts  of  the  heavy  metals, 
lead,  mercury,  and  arsenic;  occasionally  albumose,  peptones, 
lactates,  acid  lactates,  oxalates,  carbonates,  hippuric  acid,  also 
organic  compounds,  resulting  from  insufficient  or  imperfect 
oxidations,  as  amino  acids,  leucin,  tyrosin,  and  acetone  bodies. 

We  are  to  study  the  urine,  not  primarily  with  a  xdew  to  the 
diagnosis  of  renal  disease,  which  is  more  particularly  the  prov- 
ince of  the  physician,  but  to  detect  irregularities  or  deficiencies 
in  the  body  metaboHsm,  and,  as  far  as  possible,  we  are  to  study 
the  methods  whereby  we  may  correct  and  regulate  the  mal- 
nutrition which  Hes  at  the  foundation  of  many  diseases  of  the 
oral  cavity.  As  has  been  previously  stated  by  the  author,* 
if  there  are  diseases  of  the  oral  cavity  which  may  have  their 
etiology  in  some  systemic  derangement  not  easily  apparent, 
and  if  such  diseases  are  to  receive  the  attention  of  the  dentist, 
he  should  obtain  all  possible  light  on  every  case,  and  at  present 
a  quantitative  analysis  of  the  urine  is  of  greater  value  than 

*  International  Dental  Journal,  January,  1905. 
326 


PHYSICAL  PROPERTIES  OF   URINE  327 

any  other  laboratory  aid.  In  examining  a  sample  of  urine  to 
obtain  information  as  above  indicated,  it  is  essential  that  the 
sample  be  a  portion  of  the  mixed  twenty-four-hour  quantity, 
and  that  the  total  amount  of  the  twenty-four-hour  excretion 
be  known.  In  collecting  samples  for  such  analysis  a  conven- 
ient method  is  to  give  the  patient  a  one-  or  two-dram  vial, 
nearly  filled  with  water,  and  containing  three  or  four  drops  of 
a  commercial  formaldehyde  solution,  with  instructions  to  empty 
this  into  a  bottle,  or  other  receptacle,  in  which  the  twenty- 
four-hour  sample  is  collected.  Formaldehyde  if  used  in  this 
amount  has  no  effect  on  the  subsequent  analysis  and  is  a  suffi- 
cient preservative. 

Physical  Properties. 

Quantity.  —  The  quantity  of  urine  passed  in  twenty-four 
hours  normally  is  about  1200  to  1400  c.c.  for  an  adult  female 
and  100  or  200  c.c.  more  than  this  for  the  male.  The  amount 
is  increased  in  B right's  disease,  in  diabetes,  and  various  other 
pathological  conditions,  also  in  cold  weather  when  less  mois- 
ture is  given  off  from  the  skin.  Normally,  the  quantity  passed 
during  twelve  day  hours,  as  8  a.m.  to  8  p.m.,  will  exceed  the 
amount  overnight  from  8  p.m.  to  8  a.m.  In  cases  of  chronic 
interstitial  nephritis  the  twelve-hour  night  quantity  exceeds  the 
day,  hence  it  is  desirable  in  collecting  a  twenty-four-hour  sample 
to  divide  the  time  as  suggested,  and  measure  the  amounts 
separately,  especially  if  there  is  any  suspicion  of  any  chronic 
kidney  disease.  A  diminished  quantity  of  urine  may  indicate 
simply  a  diminished  amount  of  water  taken  into  the  system. 
The  urine  is  diminished  pathologically  in  acute  conditions, 
such  as  fevers,  etc.,  but  such  samples  rarely  reach  the  dental 
practitioner. 

Color.  —  The  normal  color  of  the  urine  is  usually  given  as 
straw  color  or  pale  yellow.  If  lighter  than  this  the  color  is 
regarded  as  pale,  if  darker  than  normal  it  is  regarded  as  high. 


328  URINE 

The  urine  may  also  be  colored  by  various  abnormal  constitu- 
ents; it  may  be  bright  red  from  the  presence  of  blood,  or 
chocolate  colored  with  a  so-called  coffee-ground  sediment  from 
decomposed-blood  coloring  matter.  It  may  be  brown  to  yel- 
low, bright  blue  or  green,  due  to  the  ingestion  of  various  drugs. 
If  bile  is  present  in  any  quantity  in  the  urine  it  will  have  a 
dark  or  smoky  appearance,  and,  upon  shaking,  the  foam  will 
have  a  distinctly  yellowish  or  yellowish-green  tint. 

Appearance.  —  In  addition  to  the  colors  mentioned  above 
urine  may  sometimes  have  a  smoky  appearance,  due  to  the 
presence  of  hematoporphyrin  or  iron-free  hematin,  often  found 
in  cases  of  lead-poisoning.  It  may  have  a  milky  appearance, 
due  to  presence  of  finely  divided  fat  globules,  as  in  chylous 
urine,  due  to  parasitic  disease  of  the  blood.  It  may  be  cloudy 
from  four  principal  causes:  first,  amorphous  urates;  second, 
amorphous  phosphates;  third,  pus;  and  fourth,  bacteria. 
These  may  easily  be  distinguished.  The  application  of  a  slight 
degree  of  heat  (insufficient  to  cause  coagulation  of  albumin) 
will  redissolve  the  urates,  and  clear  a  urine  which  is  cloudy 
from  this  cause.  A  deposit  of  phosphates  is  increased  by  the 
application  of  heat,  but  clears  easily  upon  the  addition  of  a 
few  drops  of  acetic  acid.  A  urine  cloudy  from  the  presence 
of  pus  is  not  cleared  by  either  of  these  methods,  but  the  cloud 
settles  with  comparative  rapidity  and  pus  corpuscles  are  easily 
recognized  by  microscopical  examination  of  the  sediment.  If 
bacteria  are  present  in  sufficient  quantity  to  cause  cloudiness, 
the  sample  is  apt  to  be  alkahne  in  reaction  and  will  not  clear 
upon  ffitering.  If  it  is  necessary  to  obtain  a  clear  solution,  a 
little  magnesium  mixture  may  be  added  to  the  urine,  then  a 
Httle  sodium  phosphate;  warm  gently  with  agitation,  when 
the  precipitated  ammonium  magnesium  phosphate  will  me- 
chanically carry  down  the  bacteria,  and  a  filtrate  may  be  ob- 
tained which,  after  acidifying  with  dilute  acetic  acid,  will  be 
suitable  for  an  albumin  test. 


PHYSICAL   PROPERTIES  OF   URINE 


329 


Specific  Gravity.  —  The  gravity  is  most  conveniently  taken 
with  a  urinomcter  (Fig.  27).  Care  should  be  taken  in  the 
selection  of  this  instrument  so  that  the  scale  graduation  may  be 
accurate.  The  fact  that  the  instrument  will  sink  in  distilled 
water  at  the  proper  temperature  (usually  60°  F.,  15^°  C.)  to 
the  zero  mark,  is  not  a  sufficient  proof  of  its  accuracy,  as  many 
cheap  instruments  will  do  this,  and  give  erroneous  readings 
at  the  higher  markings  of  the  scale.  Distilled  water  is  rep- 
resented by  1000,  and  the  relative  increase  in  the  comparative 
gravity  of  urines  will  be  easily  represented  on  the  scale  ranging 
from  1000  to  1050.  As  the  first  two  figures  of  the  specific 
gravity  are  always  the  same  (10)  they  are  usu- 
ally ,  omitted  from  the  scale  which  is  made  to 
read  from  o  to  50  or  60.  The  reading  should  be 
made,  if  possible,  from  underneath  the  surface 
of  the  liquid,  as  the  liquid  is  usually  drawn 
around  the  stem  by  adhesion,  so  that  accurate 
readings  from  the  surface  are  difficult.  The 
specific  gra\dty  of  normal  urine  is  from  1018  to 
1022;  it  decreases  in  cases  where  the  quantity  is 
much  above  the  normal  (polyurias),  unless  sugar 
is  present.  It  is  increased  by  the  presence  of 
sugar  or  by  concentration,  whereby  the  normal 
solids  are  relatively  increased.  In  case  the  quantity  of  urine 
is  too  small  for  the  determination  of  the  gra\ity  in  the  usual  way, 
the  urinopyknometer,  de\'ised  and  recommended  by  Dr.  Saxe  in 
his  "  Examination  of  the  Urine,"  may  be  employed.  See  page 
307,  on  specific  gra\'ity  of  saliva. 

Reaction.  —  The  reaction  of  urine  is  normally  acid  to  litmus- 
paper,  due  in  part  to  the  presence  of  acid  sodium  phosphate, 
and  in  part  to  organic  acid  combinations,  the  composition  of 
which  is  unknown.  The  degree  of  acidity  is  roughly  indicated 
by  the  intensity  of  color  produced  with  the  carefully  prepared 
litmus-paper.     More  accurate  results  may  be  obtained  by  a 


Fig.  27. 


330  URINE 

regular  volumetric  examination  (with  N/20  alkali),  or  by  the 
test  for  urinary  acidities  given  by  Freund  and  Topfer  who 
suggest  the  following  method: 

"  To  10  c.c.  of  the  urine  add  two  to  four  drops  of  a  1%  solu- 
tion of  alizarin.  If  the  resulting  color  is  pure  yellow,  free  acids 
are  present;  if  deep  violet,  combined  acid  salts.  If  none  of 
these  colors  appear,  there  are  present  acid  salts  of  the  type 
of  disodic  phosphate.  The  amount  of  one-tenth  normal  hydro- 
chloric acid  standard  solution  required  to  produce  a  pure  yel- 
low color  represents  the  alkahne  salts,  while  the  amount  of 
one-tenth  normal  sodium  hydrate  required  to  cause  a  deep 
violet  represents  the  acid  salts." 


CHAPTER  XXXVIII. 
NORMAL   CONSTITUENTS   OF   URINE. 

The  more  important  normal  constituents  of  the  urine  are 
urea,  uric  acid  (combined  as  urates),  chlorides,  phosphates, 
sulphates,  indoxyl,  coloring  matters;  traces  of  mucin,  organic 
acids,  carbonates,  hippuric  acid,  creatin,  and  creatinin  may  also 
be  present.  The  total  normal  soKds  are  composed  approxi- 
mately of  50%  urea,  25%  chloride  of  sodium;  at  least  one-half 
of  the  remainder  are  phosphates  and  sulphates.  We  see  that 
the  constituent  which  most  influences  the  specific  gravity  is  the 
urea,  and  in  normal  samples  the  specific  gravity  is  an  index  of 
the  amount  of  urea  present.  The  total  soHds  may  be  calcu- 
lated by  multiplying  the  last  two  figures  of  the  specific  gravity 
by  2^,*  which  will  give  approximately  the  number  of  grams  of 
soHds  in  one  liter  of  urine ;  from  this  the  solids  in  the  twenty- 
four-hour  amount  may  be  easily  calculated. 

Urea. 

The  chemistry  of  urea  has  been  already  considered   (page 

237)- 

Detection.  —  A  qualitative  test  for  this  substance  is  obvi- 
ously superfluous,  although  such  may  be  made  by  obtaining 
the  crystals  of  urea  nitrate  or  oxalate  (page  238).  The  quan- 
tity of  urea  is  of  great  importance,  especially  in  cases  where 
there  is  any  question  in  regard  to  the  body  metaboHsm  or  the 
amount  of  nitrogen  excreted.  By  far  the  greater  proportion 
of  all  nitrogenous  waste  is  eliminated  by  the  kidneys  in  the 
form  of  urea,  a  comparatively  sHght  amount  as  other  nitroge- 

*  CoefEcient  of  Hseser. 


332 


URINE 


nous  constituents  of  the  urine,  a  still  smaller  amount  in  the 
feces,  and  traces  only  by  other  avenues.  The  urea  may  be 
quantitatively  determined  by  various  methods,  the  hypobro- 
mite  method  being  the  most  practical.    See  reaction  on  page  238. 

Quantitative  Determination .  —  There  are  various  forms  of 
apparatus  used  in  connection  with  this  process. 

The  one  devised  by  Dr.  Squibb  is  pictured  in  Fig.  28.  It 
has  been  quite  generally  used;  hence  its  description  is  given. 
It  is  not  recommended,  because  a  source  of  considerable  error 


Fig.  28. 


Hes  in  the  fact  that  the  gases  (CO2  and  N)  evolved  from  the 
urea  are  very  apt  to  be  driven  over  into  bottle  A  before  all  the 
CO2  has  been  absorbed  by  the  reagent  in  B  and  consequently 
the  results  are  higher  than  they  should  be. 

The  first  step  in  the  use  of  this  apparatus  is  to  completely 
fill  the  bottle  A,  including  the  tubes  D  and  H,  with  water, 
with  the  glass  plug  E  closing  the  lower  end  of  D.  Next  put 
5  c.c.  each  of  a  40%  solution  of  caustic  soda  and  a  bromine 
solution  in  potassium  bromide  *  into  B.  Place  the  stopper  in 
B  and  connect  the  tube  C  at  //,  then  fill  accurately  the  2-c.c. 
pipette  with  urine.  Place  in  position  in  the  stopper  of  B  as 
shown  in  the  cut,  remove  E  from  the  rubber  tube  D,  and  allow 

*  For  preparation  of  this  solution  see  Appendix. 


NORMAL   CONSTITUENTS  OF   URINE 


333 


D  to  fall  to  the  hotlom  of  the  graduate  as  indicated.  Pressure 
is  now  applied  to  the  bulb  of  the  pipette,  so  that  the  2  c.c. 
of  urine  is  forced  with  moderate  rapidity  into  the  bottle.  As 
the  pressure  on  the  bulb  is  released,  water  will  be  drawn  back 
into  A,  and  it  is  essential  that  the  end  of  D  be  under  water 
during  this  part  of  the  process.  Bottle  B  should  be  agitated 
to  insure  complete  decomposition  of  the  urea.  Nitrogen  and 
carbon  dioxide  are  at  once  evolved  according  to  the  reaction  on 
page  238.  The  40%  solution  of  caustic  soda  is  strong  enough 
to  absorb  and  hold  the  CO2.  The  nitrogen  passes 
into  A ,  forcing  a  corresponding  volume  of  water 
into  the  graduate.  This  volume  of  gas,  read  in 
cubic  centimeters  of  the  water,  will  give  the 
percentage  of  urea  in  the  sample  examined,  i  c.c. 
of  nitrogen  being  equivalent  to  0.126  gram  of 
urea. 

The  Doremus-Hinds  apparatus  shown  in 
Fig.  29  gives  a  perfectly  satisfactory  method 
for  the  estimation  of  urea  by  the  hypobromite 
method.  The  reagent,  equal  parts  of  bromine 
solution  and  40%  NaOH  (x^ppendix,  page  427), 
is  introduced  into  R  and  the  tube  completely 
filled.  The  tube  U  is  next  filled  exactly  to  the  zero  mark, 
then  by  means  of  the  stop-cock  5  i  c.c.  of  urine  is  allowed 
to  enter  T  a  few  drops  at  a  time  and  slowly  enough  to  pre- 
vent any  escape  of  gas  through  R.  The  gas  rises  in  small 
bubbles  through  a  comparatively  long  tube  and  remains  in  con- 
tact with  the  reagent  which  insures  perfect  absorption  of  CO2, 
thus  overcoming  the  greatest  objection  to  the  Squibb's  apparatus. 

The  tube  T  is  graduated  to  read  centigrams  of  urea  in  i  c.c. 
of  urine.  " 

A  more  accurate  determination  of  urea  depends  upon  the 
conversion  of  urea  into  ammonia  by  various  methods  which 
make  quantitative  application  of  the  Kjeldahl  determination 


Fig.  29. 


334  URINE 

of  nitrogen.  These  are  given  in  excellent  detail  in  Hawk's 
Fifth  Edition  of  "  Practical  Physiological  Chemistry  "  and  to 
this  work  the  student  is  referred. 

Uric  Acid. 

Uric  acid  and  its  antecedents,  the  xanthin  bases,  are  derived 
from  the  decomposition  of  nuclein  and  nucleoprotein.  For 
chemistry  of  this  substance,  see  pages  240  to  243.  The  uric 
acid  is  increased  by  a  highly  nitrogenous  diet  and  certain  vege- 
table substances  which  contain  purin  (page  241)  derivatives, 
such  as  coffee,  tea,  and  cocoa.  The  so-called  red  meats,  beef, 
mutton,  etc.,  are  regarded  as  the  most  abundant  source  of  uric 
acid  and  urates.  As  previously  suggested  uric  acid  does  not 
occur  in  normal  urine  as  such,  but  is  combined  with  the  alka- 
line bases. 

Determination.  —  It  is  unnecessary  to  make  a  qualitative  test 
in  urine,  as  urates  are  always  present.  If  a  qualitative  test  is 
desired  the  murexide  test,  as  given  on  page  394,  is  available. 
Uric  acid  and  alHed  constituents  of  the  urine  are  conveniently 
determined  quantitatively  by  the  centrifugal  method  as  de- 
vised by  Dr.  R.  Harvey  Cook.*  The  detail  of  this  method  is 
as  follows:  Measure  10  c.c.  of  urine  into  a  graduated  tube, 
used  in  the  centrifugal  machine,  add  a  few  grains  of  sodium 
carbonate,  and  about  3  c.c.  of  strong  ammonium  hydrate. 
Place  in  the  centrifuge,  and  allow  to  run  for  one  or  two  mhiutes, 
then  carefully  decant  the  clear  urine  into  another  graduate 
tube,  leaving  the  precipitate  which  consists  of  earthy  phos- 
phates. The  bulk  of  this  precipitate  may  be  noticed  and  an 
idea  obtained  as  to  whether  the  earthy  phosphates  are  present 
in  normal  quantities  or  not.  To  the  clear  urine  add  2  or  3  c.c. 
of  ammoniacal  silver-nitrate  solution  (AgNOs,  5  grams;  dis- 
tilled water,  80  c.c;  strong  ammonia,  20  c.c),  and  run  in  the 
centrifuge  till  the  precipitate  of  silver  urate  has  reached  its 
*  Medical  Record,  Mar.  12,  1898,  page  373. 


NORMAL   CONSTITUENTS  OF   URINE 


335 


lowest  obtainable  reading.  The  ammonia  will  prevent  the  pre- 
cipitation of  chlorides  and,  unless  iodides  or  bromides  are  present, 
the  precipitate  will  be  fairly  pure  silver  urate,  each  tenth  of  a 
cubic  centimeter  of  the  precipitate  being  equivalent  to  0.001176 
gram  of  uric  acid  in  the  10  c.c.  of  urine  used,  or  0.01176%. 

The  silver  precipitate  is  by  no  means  pure  silver  urate,  many 
of  the  other  nitrogenous  bases  in  urine  forming  insoluble  silver 
salts.  These  occur  only  in  very  sKght  traces;  so,  for  chnical 
purposes,  the  method  is  available  unless  the  sample  contains 
bromides  or  iodides,  when  iodide  or  bromide  of  silver  will  be 
formed,  insoluble  in  the  amount  of  ammonia  usually  used. 
More  accurate  results  may  be  obtained  by  either  Hopkins'  or 
Folin's  method.  These  are  somewhat  similar  and  consist  of 
precipitation  of  the  uric  acid  as  ammonium  urate.  100  to 
200  c.c.  of  urine  is  used  and  the  precipitation  effected  by  a 
saturated  solution  of  NH4CI  (Hopkins'  method)  or  ten  grams 
ammonimn  sulphate  (Folin's  method). 

The  precipitate  is  washed  in  the  reagent  and  dissolved  in 
boiling  water  and  the  amount  of  uric  acid  determined  by  titra- 
tion with  N/20  permanganate  of  potassium.  Each  cubic  centi- 
meter of  KMn04  used  is  equal  to  0.00375  gram  of  uric  acid. 

Ammonia  Deteemtnation. 

The  amount  of  ammonia  normally  present  in  urine  is  about 
0.7  gram  in  the  24-hour  amount.  Ammonia  is  increased  in  any 
systemic  condition  resulting  in  an  increase  of  acidic  elements 
(Acidosis),  or  upon  ingestion  of  ammonium  salts  of  inorganic 
acids,  i.e.,  salts  not  easily  oxidized  to  urea. 

Normally,  the  quantity  of  NH3  follows  more  or  less  closely 
the  urea  and  the  protein  metaboHsm,  and  amounts  to  about 
one-twentieth  of  one  per  cent.  (0.05%)  or  about  0.7  gram  in 
twenty-four  hours. 

Determination  may  be  made  as  follows: 

Folin's    New    Method.  —  Measure,  by    use    of    standardized 


336  URINE 

"  Ostwald  pipette,"  i  or  2  c.c.  of  urine  into  a  large  Jena  test- 
tube.  Then  proceed  exactly  according  to  method  given  for 
saliva  on  page  310. 

Formaldehyde  Method.  —  Place  10  c.c.  urine  in  a  250  c.c. 
Erlenmeyer  flask,  add  50  or  60  c.c.  H2O,  titrate  with  N/io  NaOH 
with  phenolphthalein  as  an  indicator.  The  amount  of  NaOH 
used  will  represent  total  acidity  of  sample. 

After  exact  neutralization  add  10  c.c.  of  previously  neutral- 
ized commercial  formaldehyde  solution  and  titrate  again  with 
N/io  NaOH.     The  second  amount  of  alkali  added  represents 
ammonia  as  follows: 
4  NH4CI  -f  6  CHoO  -}-  4  NaOH  =  N4(CH2)6  +  10  H2O  +  4  NaCl. 

As  the  ammonium  salts  and  the  caustic  soda  react  molecule 
for  molecule  it  is  possible  to  make  calculation  for  quantity  of 
NH3  by  multiplying  the  N/io  factor  (0.0017)  by  the  number  of 
cubic  centimeters  of  N/io  NaOH  used. 

In  cases  of  diabetes  when  the  ammonia  reaches  a  compara- 
tively large  amount  the  figures  obtained  by  this  process  will  be 
found  to  be  a  little  high,  as  amino  acids  are  also  acted  upon  by 
the  NaOH,  and  will  be  calculated  as  ammonia,  but  for  ordinary 
work  of  clinical  comparisons  this  method  is  very  simple  and 
sufficiently  accurate. 

This  method  is  not  aflfected  by  urea,  uric  acid,  creatin,  crea- 
tinin,  purin  bases,  or  hippuric  acid.* 

Chlorides. 

The  chlorides  are  represented  in  the  urine  chiefly  by  sodium 
chloride.  This  is  present  to  the  extent  of  from  twelve  to  twenty 
grams  in  twenty-four  hours.     An  increase  above  this  quantity 

*  Dr.  Hans  Malfatti  in  Zeit.  fiir  Anal.  Chemie,  47,  page  273. 

Note.  —  See  also  the  Vacuum  Distillation  Method,  giving  very  exact  results 
when  properly  carried  out: 

H.  Bjorn  Andersen  und  Marius  Lauritzen,  Zeit.  fiir  Physiol.  Chemie,  64, 
page  21. 


NORMAL  CONSTITUENTS  OF   URINE  337 

is  unusual,  although  it  simply  indicates  an  increase  in  the  in- 
gested salt,  and  is  without  cHnical  significance.  The  chlorine 
is  diminished  in  dropsy,  acute  stages  of  pneumonia,  and  in 
fevers  generally. 

Detection.  —  The  usual  qualitative  test  with  silver  nitrate 
and  nitric  acid  is  employed  for  detection  of  chlorine  in  the  urine. 
If  one  drop  of  a  strong  solution  of  silver  nitrate  (i  to  8)  is  al- 
lowed to  fall  into  the  wine-glass  in  which  the  albumin  test 
has  been  made  (q.v.),  the  appearance  of  the  resulting  precipi- 
tate will  give  a  rough  idea  of  the  quantity  of  chlorine  present. 
If  a  soHd  ball  of  silver  chloride  is  formed  which  does  not  become 
diffused  upon  gently  agitating  the  contents  of  the  glass,  the 
chlorine  is  normal  or  increased.  If  the  precipitate  falls  as  a 
cloud  distributed  throughout  the  Hquid,  the  chlorine  is  dimin- 
ished. The  chlorine  may  be  determined  by  precipitation  with 
silver  nitrate  in  10  c.c.  of  urine,  and  the  precipitate  settled  in  a 
centrifuge-tube  to  constant  reading,  but  this  method  is  not 
recommended,  as  the  precipitate  is  a  bulky  one,  and  usually 
takes  a  long  time  for  thorough  settling.  The  titration  with 
silver  nitrate,  using  potassium  chromate  as  an  indicator,  really 
takes  less  time,  and  is  much  more  accurate.  This  titration  is 
made  in  the  usual  way  (see  page  159),  except  that,  inasmuch  as 
phosphates  and  urates  are  also  precipitated,  from  three-tenths 
to  I  c.c.  may  be  deducted  from  the  amount  of  the  silver-nitrate 
solution  used  according  as  it  is  much  or  little,  thus  allowing 
for  these  substances.  An  accurate  titration  of  chlorine  is 
described  on  page  161.  But,  as  a  rule,  the  simpler  method 
gives  results  which  for  clinical  purposes  are  equally  valuable 
with  those  of  this  more  tedious  though  more  accurate  process. 

Phosphates. 
The  phosphates  in  the  urine  are  of  two  kinds,  the  alkaline 
phosphates,'  Na2HP04  and  NaH2P04,  etc.,  and  the  earthy  phos- 
phates represented  by  the  magnesium  and  the  calcium  phos- 


338  URINE 

phates.  The  phosphates  are  normally  present  to  the  extent 
of  two  and  a  half  to  three  and  a  half  grams,  calculated  as  P2O5 
(In  twenty-four  hours). 

The  triple  phosphates,  ammonium  magnesium  phosphates 
(Plate  IV,  Fig.  2,  page  172),  are  the  forms  in  which  phosphoric 
acid  is  usually  found  in  urinary  sediment.  Crystals  of  acid 
calcium  phosphate  are  occasionally  found,  and  resemble  the 
acid  sodium  urate  in  form  (Plate  X,  Fig.  3,  page  355),  except  that 
they  are  usually  a  Httle  broader  and  more  often  occur  in  fan- 
shaped  clusters.  They  may  be  distinguished  by  treatment  with 
acetic  acid,  which  dissolves  the  calcium  phosphate  promptly, 
while  the  urate  is  slowly  dissolved  and  crystals  of  uric  acid 
appear  after  a  little  time.  The  phosphates  are  deposited  from 
neutral  or  alkaline  urines  and  when  this  precipitation  takes 
place  within  the  body,  the  crystals  cause  more  or  less  irritation 
to  the  urinary  tract  and  may  form  aggregations  which  result 
in  calculi.  Phosphates  are  supplied  by  either  a  cereal  or  meat 
diet.  They  may  be  much  increased  in  diseases  accompanied 
by  nervous  waste,  or  by  softening  and  absorption  of  bone. 
Phosphates  are  diminished  in  gout,  in  chronic  diseases  of  the 
kidney,  and  during  pregnancy. 

Detection.  —  A  qualitative  test  for  earthy  phosphates  (E.P.) 
may  be  made  by  taking  a  test-tube  half  full  of  urine,  and 
making  alkahne  with  ammonium  hydrate.  When  the  precipi- 
tate has  thoroughly  settled,  if  it  is  about  1/4  to  1/2  inch  in 
depth,  it  represents  normal,  earthy  phosphates.  If  this  mix- 
ture is  now  filtered,  the  alkaline  phosphates  (A. P.)  may  be 
determined  in  the  filtrate  by  the  addition  to  the  solution  of 
one-third  its  volume  of  magnesium  mixture.*  The  precipitate 
after  settling  will  be  1/2  to  3/4  of  an  inch  in  depth  if  normal. 
The  total  phosphates  may  be  determined  in  the  centrifugal 
machine  by  adding  5  c.c.  of  magnesium  mixture  to  10  c.c.  of 
urine.     Each  tenth  of  a  cubic  centimeter  of  the  centrifugalized 

*  See  Appendix. 


NORMAL  CONSTITUENTS  OF   URINE  339 

sediment  will  be  equivalent  to  0.00225  gram  of  P2O5  in  the  10  c.c. 
used. 

A  more  accurate  determination  of  the  total  phosphoric  acid 
may  be  made  by  the  titration  with  uranium  nitrate  or  acetate 
solution  as  follows: 

Reagents  Required.  —  First.  A  standard  uranium  solution 
may  be  prepared  as  follows:  Dissolve  35.5  grams  of  pure  ura- 
nium nitrate  or  acetate  in  about  800  c.c.  of  distilled  water; 
add  three  or  four  c.c.  of  glacial  acetic  acid  and  heat  it  enough 
to  complete  solution.  Allow  to  stand  over  night,  filter  care- 
fully, and  make  up  to  1000  c.c.  Standardize  this  solution 
against  crystalhzed  microcosmic  salt  by  dissolving  14.721  grams 
of  the  pure  salt  (NaNH  HPO4  .  4  H2O)  in  sufficient  water  to 
make  1000  c.c.  Then  titrate  20  c.c.  of  this  solution,  to  which 
has  been  added  30  c.c.  of  water  and  5  c.c.  of  sodium  acetate 
solution,  with  the  uranium  solution  (method  of  titration  is 
given  under  process  below) . 

The  uranium  solution  should  then  be  adjusted  (diluted)  so 
that  it  will  take-  exactly  20  c.c.  for  this  titration,  when  one  c.c. 
of  the  uranium  will  be  equivalent  to  five  milligrams  of  P2O5. 

Second.  A  sodium  acetate  solution  containing  100  c.c.  of 
30%  acetic  acid  and  100  grams  of  sodium  acetate  in  enough 
distilled  water  to  make  1000  c.c. 

Third.  An  indicator  consisting  of  a  saturated  solution  of 
potassium  ferrocyanide. 

Process.  —  Place  50  c.c.  of  urine  with  5  c.c.  of  sodium  acetate 
solution  above  described  in  a  small  Erlenmeyer  flask  and  heat 
nearly  to  the  boiling-point.  Titrate,  while  hot  (80°  or  above), 
with  the  standard  uranium  solution  till  a  drop  of  the  mixture 
placed  on  a  white  porcelain  tile  with  a  drop  of  the  indicator 
(K4FeCy6)  gives  a  distinct  brown  color.  This  method  of  de- 
termining the  end  point  is  known  as  "  spotting  "  and  with  a 
Httle  practice  gives  very  accurate  results. 

The  number  of  cubic  centimeters  of  uranium  solution  multi- 


340  URINE 

plied  by  o.oi  will  give  the  weight  of  P2O5  in  100  c.c.  of  urine 
(i  c.c.  of  reagent  being  equal  to  0.005  gram  P2O5). 

This  same  process  may  be  used  for  saliva  by  diluting  the 
reagent  one  part  to  five,  and  preparing  the  sample  for  titration 
as  follows:  Take  from  2  to  5  c.c.  saliva,  add  sufficient  alcohol 
to  make  10  c.c.  of  mixture,  warm,  and  filter.  This  serves  to 
separate  the  protein  substance.  Take  5  c.c.  of  the  filtered 
solution  and  titrate  with  the  diluted  uranium  solution  as  by 
the  process  given  above  for  urine.  In  this  case,  of  course,  i  c.c. 
of  the  standard  uranium  will  represent  one  milligram  of  P2O5 
rather  than  five. 

Sulphates. 

The  sulphates  in  the  urine  are  present  as  alkaline  sulphates, 
K2SO4  and  Na:S04;  also  as  ethereal  sulphates,  represented  by 
such  compounds  as  indoxyl  potassium  sulphate,  page  253. 

Detection  and  Determination.  —  The  sulphates  may  be  de- 
tected by  precipitation  with  barium  chloride  in  hydrochloric 
acid  solution.  If  the  precipitate  is  obtained  from  10  c.c.  of 
urine  and  centrifugalized  to  constant  reading,  the  per  cent,  of 
sulphuric  acid  by  weight  v/ill  be  one-fourth  of  the  volume  per 
cent,  of  the  precipitate.  The  sulphates  follow  rather  closely 
the  urea,  and  their  determination  is  not  of  great  importance. 
They  are  increased  in  acute  fevers,  diminished  in  chronic  diseases 
generally,  and  markedly  diminished  in  carbolic-acid  poisoning. 
(Ogden.) 

Determination  of  Total  Sulphur.  —  (J.  Benedict,  Biol.  Chem., 
6,  363;  W.  Denis,  J.  Biol.  Chem.,  8,  401.)  To  25  c.c.  of  urine 
contained  in  a  porcelain  evaporating  dish  (10-12  cm.  diameter) 
add  exactly  5  c.c.  of  a  solution  containing  25  per  cent,  copper 
nitrate,  25  per  cent,  sodium  chloride,  and  10  per  cent,  ammonium 
nitrate.  Evaporate  to  dryness  over  a  water-bath.  Then  heat 
over  a  flame,  gradually  increasing  the  heat  until  the  dish  is 
red  hot,  and  continue  heating  for  10  to  15  minutes.     Allow  to 


NORMAL   CONSTITUENTS  OF   URINE  34I 

cool.  Add  20  c.c.  dilute  hydrochloric  acid  and  warm  gently. 
Rinse  into  a  flask  or  beaker  by  means  of  about  100  c.c.  hot 
water.  Heat  to  boiling,  and  add  drop  by  drop  25  c.c.  of  a 
10  per  cent,  barium  chloride  solution.  Filter,  wash,  ignite,  and 
weigh. 

Coloring  Matter.  —  Urobilin,  an  important  coloring  matter 
of  the  urine,  exists  as  a  parent  substance  or  chromogen  to  which 
has  been  given  the  name  urobilinogen.  This  undergoes  de- 
composition by  action  of  Hght  with  liberation  of  urobilin. 

Urobilin  is  without  doubt  derived  from  the  bilerubin  of  the 
bile,  which,  in  turn,  comes  from  the  hemochromogen  of  the 
blood.  Dr.  J.  B.  Ogden  is  authority  for  the  statement  that  "it  is 
safe  to  infer  that  the  amount  of  urobilin  in  the  urine  is  a  meas- 
ure of  the  destruction  of  the  hemoglobin  or  blood  pigment." 

Urochrome  is  a  pigment  to  which  the  yellow  color  of  urine 
is  chiefly  due.  Uroerythrin  and  urorosein  are  less  important, 
existing  only  in  very  sHght  quantities,  but  they  are  responsible 
for  colors  of  some  sediments  and  of  decomposition  products 
which  are  noticed  in  analysis. 

Soluble  Salts. 

An  examination  of  the  soluble  salts  of  the  urine  is  easily  and 
often  profitably  made  by  simply  allowing  a  large  drop  to  evapo- 
rate spontaneously  and  examining  the  residue  with  the  micro- 
polariscope.  The  alkaline  chlorides  are  often  seen  but  they 
do  not  polarize  light.  Crystalline  phosphates,  sulphates,  urates, 
and  oxalates  do  polarize  light  and  may  frequently  be  detected 
by  their  characteristic  forms.  The  value  of  determination  of 
soluble  oxalates  in  this  way  is  suggested  on  page  356. 

Indoxyl. 

The  indoxyl  is  of  considerable  importance,  as  an  increase 
above  the  liormal  amount  is  indicative  of  increased  putrefac- 
tion of  nitrogenous  substances  (tryptophan)  taking  place  in  the 


342  URINE 

small  intestine.  Indoxyl  may  also  be  increased  by  acute  in- 
flammatory process  of  the  peritoneal  cavity.  Ordinary  con- 
stipation does  not  increase  the  indoxyl.  The  test  for  indoxyl 
depends  upon  the  oxidation  of  the  indoxyl  potassium  sulphate 
to  indigo  blue  according  to  the  following  reaction: 

2  C8H6NKSO4  +  O2  =  2  CsHsXO  +  2  KHSO4. 

Indoxyl  potassium  sulphate.  Indigo. 

Note. — As  tryptophan  is  a  necessary  constituent  of  any  nitrogenous  sub- 
stance from  which  indoxyl  is  produced,  it  may  happen  that  a  few  protein  sub- 
stances, such  as  gelatin  which  does  not  contain  trj'ptophan,  might  be  used  in 
undue  proportion  and  an  excessive  putrefaction  would  not  be  accompanied  by 
indo.xyl,  but  the  nitrogenous  food  substances  generally  contain  sufficient  trip- 
tophan to  make  the  first  statement  of  this  paragraph  practically  true. 

Detection  and  Determination.  —  15  c.c.  of  strong  HCl  is 
placed  in  a  wine-glass,  and  a  single  drop  of  concentrated  nitric 
acid  added;  then  thirty  drops  of  urine  are  stirred  into  the 
mixture.  If  indoxyl  is  present,  an  amethyst  color  develops  in 
from  five  to  fifteen  minutes.  If  the  color  is  purple,  the  indoxyl 
is  increased.  Variation  of  the  amount  of  indoxyl  within  normal 
limits  is  rather  wide,  and  the  indoxyl  may  be  reported  as  high 
or  low  normal,  increased,  or  diminished. 


CHAPTER  XXXIX. 
ABNORMAL   CONSTITUENTS   OF  URINE. 

The  principal  abnormal  constituents  are  albumin,  sugar, 
acetone,  bile,  and  various  crystalline  salts,  discoverable  either 
by  microscopical  examination  of  the  sediment,  or  by  evapora- 
tion of  a  clear  fluid,  and  examination  with  the  micropolariscope. 

Metallic  substances,  arsenic,  lead,  and  mercury  are  occa- 
sionally present,  and  tests  should  be  made  for  them  when  gen- 
eral symptoms  or  the  conditions  of  the  kidney  indicate  metallic 
poison.  Albumin  is  probably  present  in  minute  traces  in  the 
majority  of  urines.  When  in  sufficient  quantity  to  be  detected 
by  the  usual  laboratory  methods,  it  is  essential  that  we  learn 
the  source  from  which  it  has  been  derived,  for  the  simple  pres- 
ence of  even  a  considerable  trace  of  albumin  may  be  of  but 
slight  clinical  importance.  Albumin  may  indicate  either  a 
pathological  condition  of  the  kidney,  which  allows  the  entrance 
into  the  renal  tubules  of  serum-albumin  from  the  blood,  or  it 
may  indicate  a  change  in  the  composition  of  the  blood,  whereby 
the  albumin  passes  more  easily  through  the  renal  membranes, 
or  its  presence  may  be  due  to  irritations  from  various  sources 
of  the  urinary  tract;  and,  as  regards  the  bearing  of  albuminurias 
on  dental  disease,  it  is  sufficient  simply  to  determine  whether 
renal  disturbance  is  primary  or  secondary  to  some  other  trouble, 
such  as  heart  disease;  or  purely  local,  as  when  caused  by  irri- 
tation due  to  crystalline  elements. 

Detection.  —  Albumin  may  be  detected  by  either  of  two 
simple  methods.  It  is  often  desirable  to  use  both  of  these 
methods,    thereby    eliminating    possible    confusion    from    the 

343 


344  URINE 

presence  of  substances  other  than  albumin,  which  may  respond 
to  one  of  the  two  tests,  but  not  to  both. 

The  first  consists  simply  in  underlaying  about  25  c.c.  of 
filtered  urine  in  a  wine-glass  with  concentrated  nitric  acid. 
The  wine-glass  should  be  tipped  as  far  as  possible  and  the  acid 
allowed  to  run  very  slowly  down  the  side.  This  method  is 
preferable  to  the  use  of  the  apparatus  known  as  the  albumino- 
scope  or  Horismascope  (Fig.  30).    As  this  latter  method  does 


Albaoun — 


Fig.  30. 

not  provide  for  sufficient  mixing  of  nitric  acid  with  the  sample, 
the  albumin  is  shown  by  a  narrow  white  ring  at  the  plane  of 
contact  of  the  two  liquids.  A  white  ring  above  the  plane  of 
contact  is  not  albumin,  but  is  composed  of  acid  urates,  indi- 
cating an  excess  of  urates  in  the  sample  (Fig.  31  j.  The  albumin, 
in  distinction  from  this  band,  occurs  directly  above  the  acid  and 
is  usually  reported  as  the  slightest  possible  trace  when  just 
discernible;  as  a  sHght  trace,  when  well  marked,  but  not  dense 
enough  to  be  seen  by  looking  through  the  liquid  from  above; 
as  a  trace,  when  the  white  cloud  may  be  seen  by  looking  down 
into  the  glass  from  above  and  a  large  trace  if  plainly  \isible  in 
this  way. 

Acetic  acid  and  heat  method  of  .testing  for  albumin  is  the 
other  method  referred  to  in  the  preceding  paragraph.  It  is  of 
about  the  same  deUcacy  as  the  nitric  acid  test,  and  is  less  liable 
to  respond  to  substances  other  than  albumin.  It  is  made  as 
follows : 


ABNORMAL  CONSTITUENTS  OF   URINE  345 

A  test-tube  is  filled  two-thirds  full  of  perfectly  clear  filtered 
urine,  one  drop  of  acetic  acid  added  and  the  upper  half  of  the 
sample  boiled.  The  tube  can  easily  be  held  in  the  hand  by  the 
lower  end.  After  boiling,  if  the  tube  is  examined  before  a  black 
background,  a  sHght  cloudiness  or  turbidity  resulting  from 
coagulated  albumin  can  be  easily  detected  in  the  upper  part  of 
tube.  Anything  more  than  a  trace  should  be  determined  in 
the  centrifugal  machine  by  mixing  10  c.c.  of  filtered  urine 
with  about  2  c.c.  of  acetic  acid  and  3  c.c.  of  potassium 
ferrocyanide  solution.  Each  tenth  of  a  cubic  centimeter 
of  the  precipitated  albumin,  when  settled  to  constant 
reading,  indicates  one-sixtieth  of  one  per  cent,  albumin 
by  weight.  This  factor  is  fairly  correct  up  to  four-  or 
five-tenths  of  a  cubic  centimeter  of  precipitate;  beyond 
this  it  is  of  little  value,  and  the  albumin  is  best  deter- 
mined quantitatively  by  measuring  50  or  100  c.c.  of 
urine  into  a  small  beaker,  adding  a  drop  of  acetic  acid, 
and  boiling,  which  will  completely  precipitate  the  al- 
bumin. It  may  then  be  filtered  into  a  counterpoised 
filter,  thoroughly  washed,  first  in  water,  next  in  alcohol, 
and  lastly  in  ether,  dried  at  a  temperature  a  Httle 
below  the  boiling-point  of  water,  and  weighed.  Esbach's 
method  may  be  of  value  in  some  instances,  and  is  carried  out 
as  follows: 

Fill  the  albuminometer  (Fig.  32)  with  urine  to  the  line  U, 
and  then  add  the  reagent*  to  the  fine  R;  close  the  tube,  mix 
the  contents  thoroughly,  and  allow  to  stand  in  an  upright 
position  for  twenty-four  hours.  At  the  end  of  that  time  the 
depth  of  precipitate  may  be  read  by  the  figures  on  the  lower 
part  of  the  tube,  these  figures  representing  tenths  of  one  per 
cent,  of  albumin,  or  grams  of  albumin  in  a  liter  of  urine.  If  a 
sample  of  urine  contains  more  albumin  than  is  easily  estimated 

*  Esbach's  reagent  consists  of  picric  acid,  10  grams;  citric  acid,  20  grams,  and 
distilled  water  sufficient  to  make  one  liter. 


346  URINE 

by  the  centrifugal  or  Esbach's  method,  approximate  results  will 
be  obtained  by  diluting  with  several  volumes  of  distilled  water, 
until  the  quantity  of  albumin  precipitated  is  within  the  limit 
of  the  test.  The  proteoses  occasionally  occur  in  the  urine,  and 
are  distinguished  from  albumin  by  the  fact  that  they  redissolve 
at  a  boihng  temperature.  If  filtered  while  hot,  albumin,  which 
usually  accompanies  them,  will  remain  on  the  paper,  while 
albumose  will  separate  from  the  clear  filtrate  as  it  cools. 

Sugar. 

Sugar  in  urine  represents  a  perverted  process  of  oxidation 
for  which  the  pancreas  is  largely  responsible.  The  liver  also 
often  plays  an  important  part  in  cases  of  diabetes,  but  just 
how  this  is  done  is  not  clearly  known.  Sugar  in  the  urine 
does  not  of  necessity  indicate  diabetes  any  more  than  albumin 
indicates  Bright's  disease.  Many  cases  of  glycosuria  are  of  a 
temporary  nature  and  respond  readily  to  dietary  treatment. 
Whenever  sugar  is  found  it  is  desirable  to  make  tests  upon  both 
a  fasting  and  an  after-meal  sample,  such  as  might  be  obtained 
before  breakfast  and  one  hour  after  dinner.  If  the  fasting 
sample  is  comparatively  free  from  sugar,  it  indicates  that  the 
glycosuria  is  of  a  temporary  nature  and  due  to  faulty  metabo- 
Hsm,  rather  than  to  any  organic  disease  of  the  liver  or  pancreas. 

Detection.  —  Sugar  in  the  urine  may  be  detected  by  several 
general  carbohydrate  tests,  as  previously  given. 

Fehling's  test.  This  test  is  very  generally  employed  (Exp. 
167,  page  401).  It  is  best,  however,  to  modify  it  by  bringing 
the  FehHng's  solution  to  active  ebulUtion,  adding  from  five  to 
thirty  drops  of  the  suspected  sample  and  allowing  to  stand 
without  further  heating.  This  prevents  possible  reduction  of 
the  sugar  by  xanthin  bases  or  other  occasional  constituents  of 
the  urine,  which  might  give  misleading  results  if  the  mixture 
were  boiled  after  addition  of  the  sample.  There  is  less  danger 
of  trouble  of  this  sort  if  the  gravity  of  the  urine  is  below  normal. 


ABNORMAL  CONSTITUENTS  OF   URINE  347 

If  it  is  necessary  to  make  a  rapid  test,  the  mixture  may  be 
boiled  after  the  urine  is  added,  and  in  case  the  result  is  negative 
there  is  no  need  of  further  test;  if,  however,  a  slight  reduction 
of  the  copper  solution  takes  place,  it  will  be  necessary  to  repeat 
the  test,  using  the  precaution  above  given.  Quantitatively, 
sugar  may  be  determined  by  the  use  of  FehHng's  solution  as 
follows : 

If  the  urine  contains  more  than  a  trace  of  albumin,  this 
substance  should  be  removed  by  adding  a  drop  of  acetic  acid 
and  heating;  after  filtration  the  sample  should  be  cooled  and 
restored  to  original  volume  with  distilled  water.  If  specific 
gravity  of  the  urine  is  more  than  1025,  it  should  be  diluted  to 
ten  times  its  volume  with  distilled  water  (urine,  one  part;  water, 
nine).  If  the  gravity  is  less  than  1025,  dilute  it  to  five  times  its 
volume,  mix,  and  fill  a  25  c.c.  burette.  In  a  250  c.c.  flask  place 
10  c.c.  each  of  the  alkaline  tartrate  and  copper  sulphate  solu- 
tions (Fehling's  solution),  and  add  about  100  c.c.  of  distilled 
water.  Place  the  flask  over  a  Bunsen  burner,  and  bring  to  a 
boil.  If  no  change  takes  place  after  a  minute  or  two  of  boiling, 
add  the  solution  from  the  burette  gradually,  until  the  precipi- 
tate becomes  sufficiently  dense  to  obscure  the  blue  color  of  the 
solution.  Continue  to  boil  for  one  or  two  minutes,  then  re- 
move from  the  flame  and  watch  carefuUy  the  line  directly 
beneath  the  surface  of  the  Hquid,  which  will  appear  blue  until 
all  of  the  copper  has  been  reduced  to  the  red  suboxide.  The 
solution  should  be  kept  at  the  boiling-point  throughout  the 
entire  operation,  except  in  making  the  examination  of  the 
meniscus  between  the  additions  of  the  diluted  urine.  These 
additions  must  be  made  very  carefuUy,  and  as  the  process  nears 
completion  not  more  than  one  or  two  drops  should  be  added 
at  a  time.-  When  the  blue  color  has  entirely  disappeared,  and 
the  Hne  of  meniscus  has  become  colorless,  note  the  number  of 
cubic  centimeters  of  dilute  urine  used,  and  calculate  that  in 
that  quantity  there  is  an  equivalent  of  0.05  gram  of  glucose; 


348  URINE 

in  other  words,  0.05  gram  of  glucose  will  exactly  reduce  the 
amount  of  Fehling's  solution  used,  and  from  this  fact  the  amount 
of  glucose  in  the  entire  twenty-four  hour  amount  of  urine  is 
easily  calculated.  If  the  titration  is  carried  beyond  the  proper 
"  end  point "  the  meniscus  will  appear  yellow  instead  of 
colorless. 

Benedict's  test.  The  following  application  of  Benedict's  so- 
lution to  the  detection  of  sugar  in  urine  is  taken  from  a  paper 
by  Stanley  R.  Benedict  in  the  Journal  of  the  American  Medical 
Association,  October  7,  1911.  "For  the  detection  of  glucose 
in  urine  about  5  c.c.  of  the  reagent  are  placed  in  a  test-tube 
and  eight  to  ten  drops  {not  more)  of  the  urine  to  be  examined 
are  added.  The  mixture  is  then  heated  to  vigorous  boiUng, 
kept  at  this  temperature  for  one  or  two  minutes,  and  allowed 
to  cool  spontaneously.  In  the  presence  of  glucose  the  entire 
body  of  the  solution  will  he  filled  with  a  precipitate,  which  may  be 
red,  yellow  or  greenish  in  tinge.  If  the  quantity  of  glucose  be 
low  (under  0.3  per  cent)  the  precipitate  forms  only  on  cooling. 
If  no  sugar  be  present  the  solution  either  remains  perfectly 
clear,  or  shows  a  faint  turbidity  that  is  blue  in  color,  and  con- 
sists of  precipitated  urates.  The  chief  points  to  be  remembered 
in  the  use  of  the  reagent  are  (i)  the  addition  of  a  small  quantity 
of  urine  (8  to  10  drops)  to  5  c.c.  of  the  reagent,  this  being  de- 
sirable not  because  larger  amounts  of  normal  urine  would  cause 
reduction  of  the  reagent,  but  because  more  delicate  results  are 
obtained  by  this  procedure,  (2)  vigorous  boihng  of  the  solution 
after  addition  of  the  urine,  and  then  allowing  the  mixture  to 
cool  spontaneously,  and  (3)  if  sugar  be  present,  the  solution 
(either  before  or  after  cooling)  will  he  filled  from  top  to  hottom 
with  a  precipitate,  so  that  the  mixture  becomes  opaque.  Since 
bulk,  and  not  color,  of  the  precipitate  is  made  the  basis  of  a 
positive  reaction,  the  test  may  be  carried  out  as  readily  in 
artificial  light  as  in  dayhght,  tv^n  when  examining  for  very 
small  quantities  of  sugar." 


ABNORMAL   CONSTITUENTS  OF    URINE  ,  349 

The  fermentation  test  (Exp.  172,  page  401)  may  also  be  used 
to  detect  the  presence  of  sugar  and,  approximately,  the  amount. 

The  fermentation  test  for  sugar  is  a  convenient  and  easily 
made  quaHtative  test,  it  being  only  necessary  to  fill  a  fermen- 
tation tube  (Fig.  38,  page  401)  absolutely  full  of  urine  to  which 
a  small  portion  of  yeast  has  been  added,  and  to  allow  the  tube 
to  stand  in  a  warm  place  for  several  hours.  Any  collection  of 
gas  in  the  top  of  the  tube  will  indicate  the  presence  of  sugar. 
This  method  may  also  be  used  as  a  quantitative  test  for  sugar 
by  taking  two  portions  of  the  same  sample,  adding  yeast  to 
one,  and  using  the  other  as  a  control.  At  the  end  of  twenty- 
four  hours,  CO2  is  removed  from  fermented  sample,  the  specific 
gravity  of  both  samples  is  carefully  taken,  and  the  loss  of 
density  in  the  fermented  sample  is  calculated  as  sugar  by  multi- 
pl3dng  the  number  of  degrees  lost  in  gravity  by  0.23,  water 
being  considered  as  1000. 

The  phenyl-hydrazine  test  may  be  used  as  a  confirmatory  test 
or  in  cases  where  very  minute  quantities  are  suspected.  This 
test  is  considered  about  ten  times  as  deUcate  as, the  FehHng's 
test;  consequently,  it  may  show  small  amounts  of  sugar  which 
are  not  detected  by  the  more  rapid  process. 

The  optical  analysis  for  sugar  may  be  made  with  a  polariscope, 
preferably  constructed  for  use  on  urine.  This  determination 
depends  upon  the  abihty  of  glucose  to  rotate  the  plane  of  polar- 
ized light  towards  the  right,  the  degree  of  rotation  indicating 
the  amount  of  sugar  in  a  pure  solution.  Of  course,  allowance 
or  correction  must  always  be  made  for  the  presence  of  any  sub- 
stances which  will  rotate  the  light  in  the  opposite  direction, 
such  as  albumin,  levulose  and  iS-oxybutyric  acid. 

For  the  detail  of  construction  and  use  of  the  polariscope, 
the  student  is  referred  to  the  more  complete  works  on  urine 
analysis  by  Ogden,  Holland,  or  Purdy. 


350  URINE 


Acetone. 


Acetone  may  occur  in  the  urine  as  a  result  of  various  patho- 
logical conditions  and  according  to  von  Noorden  they  are  all 
due  to  some  one-sided  perversion  of  nutrition.  The  acetonurias 
attendant  on  diabetes,  scarlet  fever,  pneumonia,  small-pox,  etc., 
are  of  less  practical  interest  to  the  dental  practitioner  than 
those  more  often  overlooked  by  the  medical  profession,  and 
which  indicate  improper  diet,  possibly  resulting  in  serious 
malnutrition.  The  following  points  may  be  noted:  In  ad- 
vanced stages  of  diabetes,  acetone  appears  in  the  urine  accom- 
panied by  diacetic  acid.  An  increased  ingestion  of  proteins 
may  result  in  the  appearance  of  acetone,  in  which  case  the 
direct  cause  is  more  an  "  insufficient  utilization  of  carbohy- 
drates "  *  than  the  increase  of  protein.  Acetone  may  result 
from  the  oxidation  of  /3-oxybutyric  acid.  Diacetic  acid  is  first 
formed,  and  subsequently  the  carboxyl  group  is  replaced  by 
an  atom  of  hydrogen,  as  shown  by  the  following  graphic  formulas: 

/3-oxybutyric  acid :   CH3  -  CHOH  -  CHo  -  COOH. 
Diacetic  acid :   CH3  -  CO  -  CHo  -  COOH. 
Acetone:   CH3-CO-CH3. 

Detection.  Acetone  may  be  detected  in  the  urine  by  the 
production  of  iodoform,  as  described  under  analysis  of  saliva 
on  page  313,  but  it  is  not  in  this  case  nearly  so  delicate  a  test 
on  account  of  the  odor  and  acid  character  of  the  urine.  A 
more  useful  test  is  known  as  Legal's  test  and  is  made  as  follows: 
To  a  third  of  a  test-tubeful  of  urine  add  a  few  drops  of  a  freshly 
prepared  and  fairly  concentrated  solution  of  sodium  nitro- 
prusside,  next  add  two  or  three  drops  of  strong  acetic  acid,  and 
then  a  considerable  excess  of  ammonia.  If  the  contents  of  the 
tube  are  mixed  by  a  rather  rapid  rotary  motion  without  invert- 
ing or  violent  shaking,  the  ammonia  will  not  reach  the  bottom 

*  von  Noorden's  Diseases  of  Metabolism  and  Nutrition. 


ABNORMAL  CONSTITUENTS  OF   URINE  '         351 

of  the  tube,  and  the  presence  of  acetone  will  be  indicated  by  a 
violet-red  band  above  the  layer  of  acid  liquid.  If  much  acetone 
is  present  a  deep  violet  to  purple  color  is  obtained. 

Diacetic  Acid  occasionally  occurs  in  urine  as  an  abnormal 
constituent  most  commonly  in  advanced  stages  of  diabetes, 
usually  accompanied  by  acetone  and  /S-oxybutyric  acid.  It 
may  be  detected  by  adding  to  the  urine  a  Httle  ferric  chloride, 
when  a  dark  wine-red  color  is  produced.  If  a  precipitate  of 
ferric  phosphate  is  obtained,  filter  the  urine  and  examine  the 
filtrate  for  color.  This  test  may  be  made  fairly  distinctive  for 
diacetic  acid  by  boihng  and  cooHng  a  second  portion  of  the 
urine  previous  to  making  the  test,  when  the  result  will  be  nega- 
tive if  the  color  at  first  produced  was  due  to  diacetic  acid. 

/3-oxybutyric  Acid.  —  This  substance  usually  accompanies 
diacetic  acid  as  above  stated.  Determinations  of  the  quantity 
present  cannot  be  made  by  any  simple  method.  Perhaps  the 
most  practical  method  is  by  Bloor's  nephelometer,  page  296. 

Bile. 

Bile  may  occur  in  the  urine  as  such,  due  to  pathologic  con- 
ditions of  the  liver-  or  bile-ducts,  as  stated  on  page  322.  The 
coloring  matters  of  the  bile  may  also  occur  from  causes  aside 
from  lesions  of  the  Hver.  A  urine  containing  bile  or  bile-pig- 
ments is  always  more  or  less  highly  colored,  and  upon  shaking 
the  foam  will  be  of  a  yellow  or  greenish-yellow  color.  Albumin 
and  high  indoxyl  accompany  the  presence  of  bile  and  there  is 
also  usually  considerable  renal  disturbance.  It  may  be  de- 
tected by  carefully  adding  to  one-half  a  wine-glass  of  the  sus- 
pected sample  a  few  cubic  centimeters  of  the  alcohoHc  solution 
of  iodine  (tincture  of  iodine).  A  green  color  will  be  observed 
just  beneath"  the  line  of  contact  of  the  two  Hquids  (page  423). 
The  test  may  be  conveniently  made  by  placing  the  iodine  first 
in  the  wine-glass  and  then  with  a  pipette  introducing  the  urine 
beneath  the  iodine  solution. 


352~  URINE 

Metallic  Substances. 

Arsenic,  mercury,  and  lead  are  the  three  metals  which  it 
may  be  necessary  to  look  for  in  a  sample  of  urine.  The  method 
for  the  detection  of  mercury,  given  on  page  317,  is  applicable 
for  this  purpose. 

Arsenic  may  be  detected  by  the  Marsh-Berzelius  test  (page 
36),' after  oxidizing  all  organic  matter.  The  process  may  be 
carried  out  as  follows:  Evaporate  to  dryness  a  liter  of  urine, 
to  which  200  c.c.  of  strong  nitric  acid  has  been  added;  add  to 
the  residue,  while  still  hot,  from  15  to  20  c.c.  of  concentrated 
sulphuric  acid.  This  must  be  done  in  a  large  porcelain  evapo- 
ra ting-dish,  or  else  the  acid  must  be  added  very  slowly  to  prevent 
frothing  over  and  loss  of  a  portion  of  the  sample.  After  the 
action  has  quieted  down  the  whole  mixture  may  be  trans- 
ferred to  a  500  c.c.  Kjeldahl  flask  and  heat  applied,  gradually 
at  first,  and  then  more  strongly.  It  will  be  necessary  to  add 
from  time  to  time  small  portions  of  nitric  acid  and  possibly  a 
little  more  sulphuric  acid;  as  the  oxidation  progresses  the 
liquid  in  the  flask  becomes  Hghter  in  color  and  at  the  comple- 
tion of  the  process  is  water-white,  even  when  the  temperature 
is  increased  so  that  sulphuric-acid  fumes  are  given  off.  After 
cooHng,  the  strongly  acid  liquid  is  diluted  with  four  or  five  times 
its  volume  of  water,  filtered,  if  necessary,  to  remove  excessive 
amounts  of  earthy  sulphates,  and  is  then  ready  for  the  arsenic 
test. 

Lead.  —  The  sample  of  urine  to  be  tested  for  lead  should 
measure  at  least  1000  c.c,  and  should  be  tested  for  iodine  to 
insure  the  fact  that  the  patient  has  been  under  treatment  with 
potassium  iodide  to  dissolve  lead  salts,  otherwise  a  negative 
result  may  be  obtained  when  lead  is  actually  present  and  poison- 
ing the  system.  Oxidize  the  sample  in  precisely  the  same 
manner  as  when  making  the  arsenic  test,  up  to  the  point  of 
diluting  the  strong  acid  solution  with  water;   then,  in  this  case, 


PLATE   IX  —URINE, 


Fig.  I. 
Ammonium  Acid  Urate. 


Fig.  3.  —  Pus. 
A,  After  addition  of  Acetic  Acid. 


Fig.  2. 
Spermatozoa. 


Fig.  4. 
Renal  Casts. 


Fig.  5- 

False  Casts  and  Mucin. 


Fig.  6. 
A,  Lycopodium;  B,  Moth-scales;  C,  Cork; 
D,  Cotton-fibres;  E,  Wool-fibres. 


ABNORMAL   CONSTITUENTS  OF   URINE  '       353 

use  rather  less  water  for  the  dilution,  allow  to  cool,  and  neu- 
tralize wdth  Squibb's  ammonia,  acidify  quite  strongly  with 
acetic  acid,  and  pass  H2S  gas  into  the  solution.  It  is  desirable 
to  leave  the  solution  saturated  with  H2S  for  at  least  twelve 
hours.  Then  filter,  and  without  washing  dissolve  the  precipi- 
tate in  warm  dilute  nitric  acid,  evaporate  the  HNO3  solution 
to  dryness,  add  5  c.c.  of  water,  make  alkaline  with  a  drop  or 
two  of  ammonia,  and  again  acidify  with  acetic  acid  and  add  a 
solution  of  bichromate  of  potash.*  Allow  to  stand  several 
hours,  filter  off  the  chromate  of  lead,  wash  several  times  with 
distilled  water,  and  lastly  with  H2S  water  when  the  lead  chro- 
mate will  blacken  from  the  formation  of  lead  sulphide.  This 
stain  is  a  superficial  one  and  disappears  upon  standing,  but 
when  the  process  is  conducted  in  this  way  it  constitutes  a  very 
delicate  and  satisfactory  test  for  lead  in  either  urine  or  saHva. 

Urinary  Sediments. 

The  sediment  which  settles  from  a  sample  of  urine  upon 
standmg  consists  normally  of  a  slight  amount  of  mucin  and 
epithehal  cells.  It  may  contaui  also  bacteria  and  a  consider- 
able variety  of  extraneous  matter,  including  starch  grains, 
various  vegetables  spores,  yeast  cells,  fibers  from  various  fabrics, 
cotton,  wool,  flax  from  linen,  etc.,  diatoms,  scales  from  insects' 
wings,  and  other  particles  which  may  occur  as  dust  (see  Plate 
IX,  Fig.  6;  also  Plate  X,  Fig.  4).  Under  abnormal  conditions 
the  sediment  may  contam  crystalline  elements,  including  uric 
acid  and  urates,  phosphates,  oxalates,  cystin,  tyrosin,  leucin, 
etc.,  also  organized  elements  such  as  epithelium,  renal  or  other 
casts  (Plate  IX,  Fig.  4),  blood  globules,  pus  cells  (Plate  IX,  Fig. 
3),  spermatozoa  (Plate  IX,  Fig.  2),  fat,  mucin  (Plate  IX,  Fig. 
5),  etc.  Urinary  sediment  may  be  thrown  down  from  a  fresh 
specimen  by  the  use  of  a  centrifuge,   or  the   urine   may  be 

*  Natural  chromate  of  potash  will  precipitate  copper,  the  acid  chromate  pre- 
cipitates lead  only  of  the  second  group  metals. 


354  URINE 

allowed  to  stand  in  a  glass  tube  with  rounded  bottom  for  sev- 
eral hours,  when  the  sediment  settles  to  the  bottom  by  gravity. 
If  possible  it  is  best  to  examine  sediments  settled  in  both  of 
these  ways,  as  the  centrifuge  will  show  elements,  such  as  small 
casts,  that  would  settle  slowly,  possibly  not  at  all,  by  the  gravity 
method.  On  the  other  hand,  the  sediment  allowed  to  settle 
spontaneously  will  often  give  a  more  correct  idea  of  compara- 
tive numbers  of  the  various  elements  observed,  than  when 
settled  in  a  centrifuge-tube.  A  drop  or  two  of  formalin  may 
be  used  to  preserve  urinary  sediment,  as  suggested  on  page  327, 
but  if  too  much  of  this  substance  is  used,  especially  in  urines 
containing  high  percentages  of  urea,  a  compound  is  liable  to 
be  formed  which  has  been  called  formaldehydurea  (Plate  X, 
Fig.  5),  which  settles  with  the  sediment  and  seriously  interferes 
with  the  microscopical  examination.  This  compound  may  form 
sheaf-like  crystals  similar  to  tyrosin  and  may  be  mistaken  for 
crystals  of  sodium  oxalate,  especially  when  examined  with  a 
low  power  objective. 

Uric  Acid.  —  Uric  acid  is  deposited  from  normal  urine,  upon 
standing,  with  an  excess  of  free  acid  (HCl).  Urines  that  have 
a  high  degree  of  acidity  will  also  produce  a  like  deposit,  and  the 
finding  of  uric-acid  crystals  does  not  necessarily  signify  that 
the  crystallization  took  place  within  the  body,  unless  special 
care  has  been  taken  that  the  sample  examined  was  perfectly 
fresh,  although  the  tendency  to  deposit  uric  acid  is,  of  course, 
indicated.  The  urine  from  which  uric  acid  separates,  as  such, 
is  usually  rather  concentrated  and  of  strong  acid  reaction. 
These  crystals  vary  in  appearance  (Plate  X,  Figs,  i  and  2), 
but  are  almost  always  colored  yellow  to  red.  Colorless  crystals 
are  sometimes  observed.  They  are  usually  quite  small,  but  of 
the  peculiar  whetstone  shape  in  which  this  acid  most  usually 
crystallizes.  The  presence  of  uric  acid  has  practically  no  effect 
upon  the  acidity  of  the  sample;  for,  if  the  acid  separates  in  a 
crystalline  form,  it  is  insoluble,  and  if  it  does  not  separate  it  is 


PLATE  X.— URINE. 


Fig.  I. 
Uric  Acid. 


Fig.  3. 
A,  Sodium  Urate;  B,  Sodium  Acid  Urate. 


Fig.  2. 
Uric  Acid. 


Fig.  4. 
Yeast  Cells  and  Molds. 


Fig.  5. 
Formaldehyd  Urea  (P.  L.). 


ABNORMAL   CONSTITUENTS  OF   URINE  355 

in  combination  as  urates,  possibly,  of  course,  as  acid  urates. 
Uric  acid  exists  normally  in  proportion  to  urea  as  about  i  to  50, 
but  there  is  no  necessary  relationship  between  the  quantities 
of  the  two  substances,  and  the  one  may  be  di'minished  while 
the  other  is  increased. 

Urates.  —  Urates  may  occur  as  crystalline  or  amorphous  pre- 
cipitates. The  crystalline  urates  are  urate  of  sodium  rarely, 
acid  urate  of  sodium  (Plate  X,  Fig.  3),  and  acid  am- 
monium urate  (Plate  IX,  Fig.  i,  page  353).  The  amorphous 
urates  are  of  the  alkahne  bases,  usually  sodium,  and  are  fre- 
quently precipitated  by  lowering  of  the  temperature  after  the 
sample  has  been  passed,  in  such  cases  the  urine  assumes  a  cloudy 
appearance  which  is  cleared  up  by  the  application  of  heat.  A 
sediment  consisting  of  urates  is  usually  of  a  pinkish  color. 

Phosphates.  —  Phosphates  in  the  urinary  sediment  may  be 
amorphous  or  crystalUne.  They  are  of  the  alkaline  earths 
rather  than  of  the  alkaline  metals,  as  the  latter  are  soluble  in 
both  the  acid  and  neutral  forms.  The  amorphous  phosphates 
deposit  with  the  change  of  reaction  from  acid  to  alkaline,  and 
usually  in  the  form  of  a  so-called  triple  phosphate  of  ammonia 
and  magnesia  (Plate  IV,  Fig.  2,  page  172).  This  salt  crystallizes 
in  two  forms.  The  prismatic  form  is  the  ultimate  form;  that 
is,  if  the  crystalhzation  takes  place  very  slowly,  the  prismatic 
form  is  the  one  in  which  the  salt  is  thrown  out.  If  it  takes 
place  rapidly  it  may  be  precipitated  in  the  feathery  form,  but 
this  slowly  changes  over  to  the  prismatic  form.  The  acid 
phosphates  may  be  precipitated  closely  resembhng  in  appear- 
ance the  acid  urates  (Plate  X,  Fig.  3),  but  may  be  distinguished 
from  them  by  their  ready  solubility  in  acetic  acid  and  failure 
to  produce,  after  solution  in  acetic  acid,  any  crystals  of  uric 
acid  such  as  are  obtained  from  the  urates. 

Acid  Lactates: —  These  are  soluble  salts,  and  are  found  in 
urine  only  by  evaporation  of  a  drop  of  the  clear  fluid  and  an 
examination  of    the  residue   by  polarized  Hght.     When  found 


356  URINE 

in  the  urine,  the  significance  is  quite  different  from  that  when 
found  in  the  saHva.  as  in  the  urine  they  may  possibly  be  formed 
from  lactates,  which  indicate  a  faulty  action  of  the  liver,  and 
of  course  they  have  no  connection  with  tooth  erosion.  The 
lactates  furnish  evidence  of  similar  character. 

Oxalates,  —  Oxalates  if  found  in  the  sediment  usually  occur 
as  calcium  oxalates.  These  crystals  assume  a  variety  of  forms, 
as  shown  in  Plate  II,  Fig.  i,  page  170.  Sodium  oxalate  (Plate  II, 
Fig.  4)  may  occur  in  the  urine  (not,  however,  in  the  sediment), 
and  is  detected  only  by  evaporating  a  drop  of  the  clear  liquid 
and  examining  with  polarized  light.  Dr.  Kirk  claims  that  an 
oxaluria  may  be  detected  in  this  way  for  a  considerable  time 
before  the  appearance  of  the  oxalate  of  lime  crystals,  and  hence 
such  examination  becomes  a  valuable  aid  to  diagnosis. 

Cystin.  —  Cystin  occurs  as  six-sided  plates.  It  is  a  com- 
paratively rare  crystal,  and  indicates  insufficient  oxidation, 
particularly  of  the  organic  sulphur  compounds. 

Epithelium.  —  Epithehum  occurs  in  the  urinary  sediment 
from  any  part  of  the  urinary  tract.  In  the  male  urine  it  is 
much  easier  to  determine  the  character  of  the  epithehum  than 
in  the  female,  as  in  the  latter  the  comparatively  large  amount 
of  mucous  surface,  from  which  epithehum  may  be  gathered, 
furnishes  a  great  variety  of  forms  which  are,  of  course,  without 
cHnical  significance.  The  epithehum  from  the  vagina  may  be 
quite  readily  distinguished  as  very  large  cells  with  small  nuclei, 
lying  usually  in  masses  overlapping  one  another  but  with  com- 
paratively shght  density.  Renal  epithelium  may  be  found  as 
small,  round  cehs,  differing  but  shghtly  in  size  from  a  leucocyte. 
They  may  be  a  httle  larger,  a  httle  smaller,  or  about  the  same 
size.    They  are  round  and  more  or  less  granular  in  appearance. 

Epithehum  from  the  bladder  varies  considerably,  but  the 
majority  of  cells  would  properly  come  under  the  general  head 
of  squamous  epithehum,  rather  large  and  flat  with  a  distinct 
nucleus  of  medium  size.    Epithehal  cells  from  the  neck  of  the 


ABNORMAL  CONSTITUENTS  OF   URINE  ■    357 

bladder  in  male  urine  are  quite  t>^ical,  being  round  and  com- 
paratively dense  with  a  prominent  nucleus.  They  are  four 
or  five  times  the  size  of  a  leucocyte  and,  in  case  of  irritation 
at  the  neck  of  the  bladder,  are  usually  present  in  considerable 
numbers  and  of  quite  uniform  appearance. 

Renal  casts  consist  of  molds  formed  within  the  tubules  of 
the  kidneys  which  retain  the  form  of  the  tubules  after  expul- 
sion into  the  bladder.  According  to  Ogden  the  most  probable 
theory  of  their  formation  is  "  that  they  are  composed  of  coagu- 
lable  elements  of  blood  that  have  transuded  into  the  renal 
tubules,  through  pathologic  lesions  of  the  latter,  and  have  there 
solidified  to  be  later  voided  with  the  urine,  as  molds  of  the 
tubules."  Casts  are  termed  blood  casts,  pus  casts,  epithelial 
or  fat  casts  according  as  these  elements  may  adhere  with  more 
or  less  profusion  to  the  cast  itself.  Pure  hyahne  casts  are  pale, 
perfectly  transparent  cyhnders,  with  at  least  one  rounded  end 
which  can  be  plainly  seen,  and  may  occur  occasionally  in  urine 
from  perfectly  healthy  individuals.  Fibrinous  casts  are  highly 
refractive  and  when  seen  by  white  Hght  are  of  a  yellowish  color 
and  indicate  acute  and  renal  disturbance.  Waxy  casts  re- 
semble the  fibrinous  casts  as  regards  density,  but  they  have 
no  color,  and  usually  indicate  advanced  and  serious  stages  of 
kidney  disease,  while  the  presence  of  fibrinous  casts  has  no 
necessarily  serious  significance. 

Blood  and  Pus  are  readily  recognized  under  the  microscope 
after  a  very  Httle  practice.  The  blood  disks  are  circular  and 
show  a  characteristic  biconcavity  in  the  alternate  shading  of 
the  edge  and  center  by  slight  changes  of  focus.  The  red  cor- 
puscles usually  show  a  shade  of  color  by  white  light.  The  pus 
corpuscles  or  leucocytes  are  larger  than  the  red  corpuscles,  and 
are  granular  in  appearance.  Treatment  with  acetic  acid  de- 
stroys the  granular  matter  and  .brings  into  prominence  the 
cell  nuclei,  two  or  three  in  number.  If  the  leucocytes  are  free 
and  scattered  they  should  not  be  regarded  as  pus  but  be  re- 


358  URINE 

ported  simply  as  an  excess  of  leucocytes;  if  they  are  very 
numerous  and  occur  in  clumps  they  constitute  pus. 

Spermatozoa.  —  Occasional  spermatozoa  may  be  found  in 
sediment  from  either  male  or  female  urine  and  are  without 
clinical  significance.  If  persistent  and  in  considerable  numbers, 
seminal  weakness  is  indicated  (Plate  IX,  Fig.  2,  page  353). 

Fat  occurs  in  urinary  sediment  as  small  globules,  highly 
refractive  and  varying  greatly  in  size.  They  are  frequently 
adherent  to  cells  or  to  casts.  Fatty  casts  indicate  a  fatty  de- 
generation, which  may  or  may  not  result  from  chronic  disease. 
Fat  may  be  demonstrated  by  staining  with  osmic  acid  which 
is  reduced  by  the  double-bonded  fatty  constituent  (olein), 
leaving  a  black  deposit  which  stains  the  globule. 

Mucin  appears  in  the  sediment  as  long  and  more  or  less 
indistinct  threads.  An  excessive  amount  usually  indicates  irri- 
tation of  some  mucous  surface.  The  source  would  have  to  be 
determined  by  other  more  characteristic  elements  (Plate  IX, 

Fig-  5)- 

The  salts  which  may  be  obtained  by  evaporation  of  a  drop 
of  clear  urine  and  detected  by  the  micropolariscope  are  similar 
to  those  occurring  in  the  saHva;  sodium  oxalate  is  probably 
most  frequently  found.  If  the  gra\'ity  is  above  normal  the 
urea  often  crystallizes,  making  it  somewhat  difficult  to  pick 
out  the  abnormal  crystalline  constituents.  Phosphates  are 
also  usually  observed,  but  these  crystals  are  large  and  as  a  rule 
prismatic,  not  easily  mistaken  for  anything  else. 

Recording  Results. 
As  stated  at  the  beginning  of  the  chapter  on  urine,  our  object 
has  been  the  study  of  this  secretion  from  the  standpoint  of 
general  metaboHsm,  rather  than  with  a  view  to  differentiate 
various  forms  of  renal  disease,  and  while  it  is  important  that  the 
presence  of  renal  disease  should  be  recognized,  its  further  in- 
vestigation constitutes  a  proper  study  for  the  physician  rather 


ABNORMAL   CONSTITUENTS  OF    URINE 


359 


than  for  the  dentist,  and  when  such  conditions  are  found  to 
exist  a  patient's  physician  should  be  apprised  of  the  fact. 

Uniformity  of  method  in  making  out  report  cards  is  desirable 
although  not  absolutely  necessary  for  the  best  class  work; 
hence  a  few  suggestions  as  to  the  use  of  the  following  blank. 
If  no  test  is  made,  make  no  entry  whatever  on  the  blank.  This 
permits  the  use  of  a  dash,  "— ",  to  indicate  a  diminished  (less 
than  normal)  quantity.  If  a  substance  is  present  in  normal 
quantity  use  a  capital  "  N,"  if  increased  above  normal  amount 
use  "+."  If  absent  use  abbreviation  "  abs.,"  never  the  dash 
or  minus  sign.  Observance  of  this  method  greatly  facilitates 
correction  of  the  report  slips. 


U.  No. 

Urine  Analysis  by 

Name 

Date 

24  h.  Am't. 

Urea 

Grams  in  24  hours. 

Sp.  Gr. 

React.                 Uric  Ac. 

"       %.= 

Color 

Appear.               Ammon. 

%,=  , 

Ind. 

E.  Phos.           "  Chlor. 

%,=                             '     ' 

Bile 

A.  Phos.              Phos.  Ac. 

%,=        . 

Diac.  Ac. 

Acetone               Sugar 

%,= 

Alb. 

Uric  Ac.  to  Urea 

=  I  to 

Soluble  Salts 

(cryst.) 

Sediment 

-— 

r- 

' 



360  URINE 

It  is  often  convenient  to  file  analyses  by  "  Case  "  number. 
This  will  always  be  the  same  and  results  of  urine  analyses, 
saliva  analyses,  physical  examination  of  the  patient,  diet  lists 
and  important  letters  may  be  brought  together  forming  a  com- 
plete story  of  the  case. 

The  following  sahva  blank  has  been  arranged  to  facilitate 
the  comparison  of  quantities  of  the  sulphocyanates  and  am- 
monia salts,  of  albumin  and  mucin,  and  of  oxidases  and  nitrites. 
The  common  algebraic  sign  of  inequality  is  serviceable  here. 
«■  ». 


S.  S.                    Date                                    Name 

SALIVA            Analysis  for 

Appearance                    Odor                             Acidity 

Alkalinity 

Spedfic  gravity                                 Mucin 

Albumin 

Ammonium  Salts                              HCNS 

Ptyalin 

Chlorine                                        Glycogen  test 

Phosphates 

Acetone                                              Nitrites 

Oxydase 

Soluble  salts  by  polarized  light 

Viscosity 

Sediment 

Remarks: 

CHAPTER  XL. 
METABOLISM. 

It  has  been  too  much  the  practice  to  study  a  single  relation 
and  jump  at  conclusions  without  regard  to  co-relation  of  factors 
which  may  not  appear  to  be  closely  allied  but  which  nevertheless 
exert  important  influences.  Witness  the  effort  to  establish  the 
relation sliip  of  tartar  deposition  to  calcium  content  of  the  saliva 
without  considering  the  quantity  of  carbon  cUoxide  present  or 
the  fact  that  certain  colloidal  substances  (such  as  occur  in  saliva) 
may  prevent  precipitatiDn  of  calcium  salts. 

The  relations  of  potassium  sulphocyanate  to  dental  caries, 
and  other  problems  have  been  studied  in  much  the  same  way, 
and  the  object  of  this  chapter  is  to  emphasize  the  necessity  of 
getting  all  possible  viewpoints  of  a  given  question  before  attempt- 
ing to  draw  positive  conclusions  regarding  it.  "     • 

It  is  conceded  that  the  general  systemic  condition  may  be  an 
important  factor  in  the  success  of  oral  treatment  by  the  dentist. 
In  other  words  it  is  worth  while  to  know  something  of  the  general 
condition  of  the  patient  in  addition  to  the  knowledge  obtained 
by  the  local  examination. 

jMetaboHsm  is  an  inclusive  term  indicating  the  chemical 
changes  whereby  the  body  utilizes  the  nutritive  elements  of  the 
food.  It  may  be  considered  in  two  divisions  as  constructive 
metabolism,  anabolism,  or  synthetic  processes,  and  destructive 
metabolism,  catabolism,  or  analytic  processes. 

We  have  studied  the  cleavage  of  complex  food  molecules  as 
carried  on  by  the  digestive  processes  but  they  are  here  by  no 
means  complete'.  How  far  the  cell  carries  analysis  of  digestive 
products  is  unknown,  possibly  to  very  simple  forms,  but  we  know 
that  the  analytical  process  is  continued  and  subsequently  exten- 

361 


362  METABOLISM 

sive  and  complex  syntheses  result  in  the  building  and  repair  of 
tissue.  The  food  material  upon  which  tissue  building  and  heat 
production  depend  may  be  classified  as  of  four  kinds,  Protein, 
Fat,  Carbohydrates,  and  Mineral  Salts. 

In  considering  the  utihzation  of  these  substances  by  the 
system  we  are  obliged  to  content  ourselves  with  a  very  general 
outline  and  a  few  definitions.  We  have  suggested  the  dual 
nature  of  metabolism  resulting  in  the  maintenance  of  heat  and 
repair  of  tissue,  but  we  have  come  to  accept  the  measure  of  food 
value  as  expressed  in  terms  of  heat  production  alone.  This 
method  may  not  be  ideal  but  as  yet  we  have  no  unit  of  value 
which  will  measure  the  usefulness  of  all  four  kinds  of  food  ma- 
terial. The  unit  generally  used  is  the  calorie,  which  may  be 
defined  as  the  degree  of  heat  necessary  to  raise  one  kilo  of  water 
one  degree  centigrade,  and  is  a  thousand  times  as  great  as  the 
small  calorie  (seldom  used). 

The  combustion  of  one  gram  of  fat  furnishes  a  heat  equivalent 
of  nine  and  three  tenths  calories,  while  a  gram  of  either  pure 
carbohydrate  or  protein  will  furnish  four  calories.  These  figures 
are  not  absolutely  accurate  because  of  slight  discrepancies  be- 
tween the  combustion  of  metabolism  and  the  combustion  of  the 
colorimeter  but  they  are  accepted  as  the  basis  for  computation. 

An  average  adult  male  doing  average  work  neither  wholly 
sedentary  nor  wholly  muscular  will  require  perhaps  2500  calories 
per  day.  This  should  be  made  up  of  a  "balanced"  diet  consist- 
ing approximately  of  eighty  grams  of  protein,  one  hundred  and 
twenty  grams  of  fat  and  three  hundred  grams  of  carbohydrates. 
The  digestibility  and  adaptability  of  food  should  also  receive 
careful  attention,  but  as  this  is  largely  a  matter  of  individual 
peculiarities  tables  and  rules  are  impractical.  As  an  illustration 
of  this  fact  take  salt  pork  and  bacon  containing  similar  percent- 
ages of  fat,  and  yielding  about  the  same  number  of  calories,  but 
the  one  is  very  indigestible,  the  other  is  often  used  in  the  diet 
of  invalids  or  small  children. 


METABOLISM  363 

The  calorie  requirement  per  kilo  of  body  weight  for  an  adult 
doing  average  work  is  about  thirty-five,  for  children  it  is  much 
greater  than  this. 

Fat.  —  The  fat  molecule  does  not  necessarily  undergo  decom- 
position (cleavage)  to  the  same  extent  as  either  the  protein  or 
carbohydrate  molecule;  that  is,  albumin  of  the  egg  must  be 
resolved  to  very  simple  forms  and  a  new  albumin  molecule  be 
built  up  before  it  can  be  absorbed  and  utiUzed,  while  fat  from 
one  animal  can  be  recovered  as  such  from  the  tissues  of  another; 
the  second  having  used  the  first  for  food. 

According  to  Taylor  (Digestion  and  Metabolism)  the  mole- 
cule of  stearic  acid  passes  through  various  acids  of  the  series,  the 
chain  splitting  each  time  at  the  beta  carbon  till  butyric  acid  is 
reached.  From  this  point  the  cataboHsm  proceeds,  in  part,  in 
the  same  way  as  before  resulting  in  formic  acid,  CO2  and  H2O, 
but  from  butyric  acid  we  may  also  obtain  the  beta  oxybutyric 
acid,  diacetic  acid  and  acetone.  Normal  fat  metabolism  is 
dependent  upon  the  simultaneous  metabolism  or  combustion  of 
carbohydrates,  that  is,  the  absence  of  carbohydrates  results  in 
acidosis  due  to  imperfect  oxidation  of  fat  and  consequent  forma- 
tion of  the  acetone  bodies. 

Protein  metabolism  results  in  the  splitting  of  the  complex 
protein  molecule  with  the  formation  of  amino  acids.  Some  of 
these  such  as  glycerol,  alanin  and  aspartic  acid  are  capable  of 
producing  carbohydrates,  others  like  tyrosin  and  histidin  are  not. 
The  cleavage  of  some  amino  acids  splits  off  urea,  but  in  a  much 
larger  number  of  cases  such  cleavage  results  in  the  formation  of 
ammonia  which  then  unites  with  water  and  carbon  dioxide 
forming  urea. 

Carbohydrates.  —  The  present  concept  of  carbohydrate  metab- 
olism is  givert  by  Dr.  Percy  G.  Stiles  in  the  Boston  Medical  and 
Surgical  Journal  for  April,  191 7.  From  this  article  we  abstract 
the  following  brief  conclusions : 

Carbohydrates  after  digestion  and  absorption  are  found  in 


364  METABOLISM 

the  blood  stream  as  blood  sugar  (glucose) .  This  sugar  is  oxidized 
by  the  muscles,  resulting  in  the  production  of  lactic  acid,  the 
presence  of  which  causes  fatigue.  During  relaxation  this  lactic 
acid  is  reincorporated  in  an  undetermined  "precursor"  which 
had  been  responsible  for  its  production  in  the  first  place. 

Concerning  the  role  of  the  pancreas  in  carbohydrate  metab- 
olism Stiles  says,  "A  function  of  this  organ  even  more  necessary 
than  its  digestive  contribution  is  the  delivery  to  the  blood  of  the 
hormone  which  makes  it  possible  for  the  muscles,  including  the 
heart,  to  oxidize  sugar.  Abundance  of  this  hormone  insures  a 
high  tolerance  for  sugar;  want  of  it  produces,  according  to  the 
degree  of  the  lack,  a  low  tolerance  or  substantial  inability  to  make 
use  of  carbohydrate." 

Mineral  Salts.  —  A  well-balanced  diet  will  furnish  the  proper 
amounts  of  mineral  solids  (excepting  perhaps  sodium  chloride) 
but  all  diets  are  not  balanced  and  it  is  well  to  know  what  part  the 
various  salts  have  in  maintaining  the  health  of  the  individual. 

Sodium  chloride  is  essential  to  digestion  because  it  has  been 
repeatedly  demonstrated  that  if  sodium  chloride  is  withheld 
hydrochloric  acid  will  not  enter  the  stomach.  Excess  of  sodium 
chloride  may  cause  irritation  or  place  an  undue  strain  upon  weak 
or  diseased  kidneys  and  in  such  cases  should  be  avoided;  on  the 
other  hand  acidosis  usually  results  from  a  salt-free  diet. 

Potassium  salts  are  said  to  keep  the  tissues  soft  and  pliable, 
to  prevent  hardening  of  the  arteries,  etc.,  but  potassium  salts 
may  cause  a  diminution  of  necessary  sodium  according  to 
Bunge  (Physiologic  and  Pathologic  Chemistry,  2nd  Edition), 
who  says  that  potassium  salts  will  react  with  sodium  chloride 
in  the  system  forming  potassium  chloride  and  undesirable  sodium 
salts,  both  of  which  are  eliminated,  by  the  kidneys  and  thus  cause 
loss  of  sodium. 

Tibbies  quotes  Cahn  in  Zeit.  f.  Physiol.  Chem.  in  practically 
the  same  statement. 

Calcium  salts  in  considerable  quantities  are  essential  during 


METABOLISM  365 

childhood  and  in  fact  as  long  as  calcification  of  any  sort  is  a 
necessary  process  (as  in  pregnancy) .  In  old  age  the  system  needs 
but  little  calcium.  Tibbies  says  that  daily  diet  should  include 
one  to  one  and  one-half  grams  of  calcium  oxide,  and  care  should 
be  taken  that  it  is  not  lost  as  oxalate. 

H.  C.  Hartwig  in  the  International  Journal  of  Orthodontia 
finds  a  direct  relationship  between  the  calcium  content  of  the 
sahva  and  caries  in  pregnant  women.     Cosmos  191 7,  page  665. 

Magnesium  occurs  generally  distributed  in  the  system,  the 
bones  containing  about  one  per  cent.  By  increasing  the  amount 
of  magnesium  ingested  the  percentage  in  the  bone  may  be 
increased  but  it  does  not  take  the  place  of  calcium.  The  com- 
pounds of  magnesium  are  generally  more  soluble  than  those  of 
calcium.  IMagnesium  oxide,  as  milk  of  magnesia,  is  used  exten- 
sively as  an  antacid.  An  excessive  amount,  however,  may  act 
in  removing  necessary  calcium  in  just  the  same  way  that  potas- 
sium acts  in  remo\ing  sodium,  as  indicated  by  the  following  from 
Pickerills'  Prevention  of  Dental  Caries  and  Oral  Sepsis,  page  120. 

"Weiske's  experiments  also  support  these  findings.  For 
instance,  of  two  rabbits,  one  received  one  gram  CaCOa  daily  in 
addition  to  its  food;  the  other  one  gram  of  MgCOs  for  three 
months.  The  rabbits  were  then  killed,  and  it  was  found  that, 
although  they  were  of  equal  body-weight,  the  total  weight  of 
the  bones  (dried  and  fat-free)  in  the  first  rabbit  exceeded  that  of 
the  second  rabbit  (77.45  grams  :  69.52  grams) ;  and,  further,  that 
the  amount  of  organic  matter  in  the  bones  of  the  MgCOa  rabbit 
was  in  excess  of  that  in  the  CaCOs  rabbit." 

Iron  is  an  essential  constituent  of  blood  derived  from  food, 
and  perhaps  more  than  in  the  case  of  any  other  mineral  con- 
stituent, it  is  necessary  for  iron  to  be  taken  in  natural  organic 
combination. 

Phosphates  are  essential  for  the  development  of  all  cellular 
tissue.  Phosphates  are  credited  with  preventing  the  deposition 
of  uric  acid  by  the  reaction  on  page  242,  also  with  keeping 


366  METABOLISM 

calcium  oxalate  in  solution.     Phosphate  acts  beneficially  in  the 
bowels  by  slightly  stimulating  the  peristaltic  action. 

Iodine  occurs  in  the  ductless  glands,  and  is  apparently 
necessary  for  their  best  development,  although  this  fact  has  been 
seriously  questioned. 

It  is  impracticable  to  give  tables  of  food  composition,  but  the 
following  may  be  noted: 

Strawberries,  beans  and  potatoes  are  rich  in  potassium 
compounds;  beets,  spinach,  turnips  and  cherries  are  rich  in 
sodium  salts;  milk,  oranges,  turnips  and  parsnips  are  rich  in 
calcium  oxide;  almonds  and  walnuts  are  rich  in  mangesium 
oxide;  carrots  and  rice  are  rich  in  iron;  meat,  cheese,  beans, 
eggs  and  wheat  are  rich  in  phosphates;  coca  powders,  rhubarb, 
and  spinach,  are  rich  in  oxalates. 

Vitamines.  —  In  regard  to  these  substances  we  quote  again 
from  Doctor  Stiles:  "Five  years  ago  the  emphasis  in  this  sphere 
(the  field  of  nutrition)  was  upon  the  variable  value  of  proteins 
from  different  sources.  It  appears  largely  to  have  shifted  to  the 
importance  of  minor  constituents  of  the  diet.  The  view  that 
beriberi,  scurvy,  and  perhaps  pellagra  are  deficiency  diseases, 
in  the  sense  that  they  are  caused  by  the  failure  of  the  food  to 
provide  certain  specific  compounds  which  are  required  for  normal 
maintenance,  is  generally  familiar.  It  was  at  first  proposed  to 
describe  these  essential  substances  as  vitamines.  The  term 
would  imply  that  they  were  nitrogenous  and  of  a  fixed  molecular 
type.  It  has  been  thought  better  to  call  them  merely  accessory 
substances.  This  does  not  commit  one  to  any  narrow  conception 
of  their  chemical  nature." 


EXPERIMENTS. 

EXPERIMENTS   FOR   CHAPTER  I. 

If  possible  it  is  highly  desirable  to  spend  a  little  time  in 
reviewing  the  principles  which  form  a  necessary  foundation  for 
any  kind  of  chemical  specialization.  These  are  supposed  to  have 
been  studied  in  High  School  course,  but  in  the  author's  experi- 
ence many  students  enter  upon  the  study  of  dentistry  not 
directly  from  High  School  graduation  but  after  a  lapse  of  one, 
two,  or  more  years.  Hence  a  few  experiments  are  introduced 
suitable  to  accompany  such  a  lecture  review  as  suggested  above. 

Oxidation  and  Valence. 

Exp.  I.  Weigh  carefully  a  porcelain  crucible.  Then  weigh 
into  it  about  one  gram  of  clean  copper  turnings.  Heat  strongly 
for  about  fifteen  minutes ;  then  cool  and  weigh.  Explain  in- 
crease of  weight  and  compare  result  obtained  with  theoretical 
result,  assuming  that  the  entire  amount  of  copper  had  been 
oxidized. 

Exp.  2.  To  a  solution  of  potassium  chlorate  add  a  little 
sulphurous  acid  and  boil.  Test  the  sulphurous  acid  for  sul- 
phuric acid  (H2SO4)  before  starting  and  after  completing  the 
experiment. 

Exp.  3.  Prepare  some  chlorine  water  as  follows:  Into  a 
test-tube  drop  some  crystals  of  KCIO3.  Add  a  few  c.c.  of  strong 
HCl,  just  enough  to  cover  the  crystals.  Allow  the  evolution  of 
gas  to  become  fairly  brisk  and  fill  tube  three-quarters  full  of 
water. 

KCIO5  +  2  HCl  =  KCl  +  CH-  ClOo  +  H2O. 

Caution.  '  Avoid  heating,  as  in  this  reaction  oxides  of  chlorine 
are  formed  which  are  liable  to  explode  if  heated. 

367 


368  EXPERIMENTS 

Avoid  the  escape  of  CI  gas  into  the  laboratory  as  far  as 
possible. 

Exp.  4.  Warm  a  little  sulphurous  acid  solution  with  a  few 
drops  of  the  chlorine  water  just  prepared,  testing  for  H2SO4  as 
in  Exp.  2. 

Exp.  5.  To  a  dilute  solution  of  potassium  ferrocyanide  add 
some  strong  chlorine  water,  and  warm.  After  ten  or  fifteen 
minutes  test  for  the  presence  of  ferrocyanide  with  dilute  ferric 
chloride.     Explain. 

Crystallization  and  Solution. 

Exp.  6.  Make  hot,  nearly  saturated  solutions  of  each  of  the 
following:  potassium  bichromate,  sodium  chloride,  potassium 
nitrate.  Turn  off,  or  filter,  the  clear,  hot  solutions  and  allow  to 
cool.  When  they  have  nearly  reached  the  room  temperature, 
again  decant  the  clear  solutions  and  place  in  ice  water  until 
thoroughly  cold.  Compare  the  effects  of  the  temperature  on 
the  solutions  of  the  three  salts. 

Exp.  7.  Wrap  a  few  crystals  of  KMn04  in  a  piece  of  filter 
paper  and  suspend  in  the  top  of  a  test  tube-full  of  water.  Infer- 
ence regarding  gravity  of  solution? 

Exp.  8.  Mix  equal  volumes  of  ether  and  water  in  a  test-tube. 
Shake  gently,  allow  to  separate  completely.  Remove  a  portion 
of  the  ether  and  test  for  water  with  anhydrous  CUSO4. 

Exp.  9.  Into  the  25  c.c.  graduate  in  your  desk,  measure  as 
accurately  as  possible  15  c.c.  of  alcohol.  Into  a  second  graduate 
measure  in  like  manner  10  c.c.  of  water  and  add  it  slowly  to  the 
alcohol  in  the  first  graduate.  Stir  carefully  with  a  glass  rod. 
Note  change  in  temperature  if  any.  Note  volume  of  mixed 
liquids  and  explain. 

Exp.  10.  In  a  test-tube  dissolve  a  small  crystal  of  iodine  in 
one  or  two  cubic  centimeters  of  alcohol.  Note  color  of  solution. 
Add  ten  cubic  centimeters  of  water  and  explain  appearance  of 
the  iodine  solution.     Now  add  five  to  ten  cubic  centimeters  of 


OSMOSIS  AND  DTALVSTS 


369 


chloroform,  close  tube  with  thumb  and  turn  over  several  times. 

Explain  results. 

Osmosis  and  Dialysis. 

Exp.  II.  The  student  may  satisfactorily  demonstrate 
osmotic  pressure  for  himself  by  the  use  of  the  following  experi- 
ment : 

Prepare  a  substitute  for  the  usual  semipermeable  cup  by 
taking  the  ordinary  dialyser  parcliment  tubing.  Soak  first  in 
warm  water  and  then  in  a  dilute  solution  (2%)  of  potassium 
ferrocyanide.  Allow  to  become  nearly  dry  and  then  soak  in  a 
dilute  solution  of  copper  sulphate.  Allow  the  tube  to  become 
nearly  dry  again,  then  wash  once  or  twice  with  warm  water. 

With  dialyser  tubing  thus  prepared,  a  small  bag 
or  pouch  capable  of  holding  10  or  15  c.c.  can  be  made 
and  tied  very  tightly  to  one  end  of  a  piece  of  glass 
tubing  four  or  five  inches  long  with  an  internal 
diameter  of  three  or  four  millimeters. 

Fill  the  parchment  bag  with  sugar  solution  and  then 
introduce  a  pre\dously  selected  capillary  tube  which 
fits  into  the  larger  tube  rather  closely.  Seal  joints  A 
and  B  (Fig.  33)  with  paraffin  and  suspend  the  bag  in 
a  beaker  of  distilled  water.  Watch  the  level  of  the 
liquid  in  the  capillary  tube. 

Exp.  12.  In  a  dialyzing  tube  (Fig.  26,  page  316) 
place  a  solution  of  NaCl.  In  another  dialyzing  tube 
place  a  solution  of  egg  albumin;  set  the  tubes  in 
separate  small  beakers  of  distilled  water.  After 
several  hours  standing  test  the  distilled  water  in  the 
first  beaker  for  salt  by  adding  a  Httle  silver  nitrate  solution, 
and  test  the  water  in  the  second  beaker  for  albumin  by  boiling 
with  a  drop  of  acetic  acid.  Compare  results  of  these  tests 
with  similar  tests  made  with  known  solutions  of  salt  and  of 
albumin. 


370  EXPERIMENTS 

Neutralization  and  Hydrolysis. 

Exp.  13.  Add  a  dilute  solution  of  caustic  potash  to  5  c.c. 
of  nitric  acid  diluted  with  twice  its  bulk  of  water,  until  the 
mixture  turns  litmus  paper  neither  red  nor  blue.  Without 
boiUng  evaporate  the  solution  in  a  porcelain  dish.  Test  with 
glass  rod  until  a  drop  hardens  as  it  cools,  and  becomes  almost 
soUd.     Then  let  entire  solution  become  cold. 

Note  three  diflerences  in  the  substance  produced  by  this 
experiment  from  either  of  the  original  substances  used. 

Write  in  your  laboratory  notebook  the  following  neutraliza- 
tion reactions: 

1.  Ammonium  hydroxide  and  nitric  acid. 

2.  Sodium  hydroxide  and  nitric  acid. 

3.  Ammonium  hydroxide  and  oxahc  acid. 

4.  Sodium  hydroxide  and  oxahc  acid. 

5.  Sodium  hydroxide  and  nitrous  acid. 

Exp.  14.  Rose's  Reaction.*  —  Color  a  solution  of  borax, 
(M/io)  with  Htmus  solution,  then  add  acetic  acid  very  carefully 
till  the  litmus  just  turns  pink.  Now  dilute  largely  by  turning 
into  distilled  water  when  the  color  again  becomes  blue  due  to 
increased  hydrolyzation  of  the  borax. 

Exp.  15.  Place  2  c.c.  of  M/io  solution  of  borax  in  each  of 
two  small  beakers,  add  to  one  a  few  drops  of  HgXOs,  and  to  the 
other  a  few  drops  of  AgXOs  solution.  Note  the  color  of  the 
precipitate  in  each  case. 

In  each  of  two  larger  beakers  place  50  c.c.  of  water  with  five 
or  six  drops  fi/2  c.c.)  of  the  above  borax  solution,  then  to  one 
add  a  few  drops  of  HgNOs  solution,  and  to  the  other  some  AgNOa 
solution  till  a  precipitate  is  produced.  Note  color  of  precipitate 
in  each  case  ('HgjO  and  AgoO  are  produced). 

Now  dilute  the  mixture  in  the  first  two  beakers  (containing 
precipitate  of  borates)  with  50  c.c.  of  water.     Stir  and  allow  to 

*  Holleman-Cooper,  Inorganic  Chemistry. 


PEROXIDES  '       371 

stand  ten  minutes.  Draw  inference  regarding  hydrolysis  of 
borax,  also  regarding  relative  stability  of  the  borates  of  silver 
and  mercury. 

Equilibrium  and  Ionization. 

Exp.  16.  To  5  c.c.  of  a  tenth  molar  solution  of  ferric  chloride 
add  15  c.c.  of  a  tenth  molar  solution  of  KCNS.  Dilute  a  portion 
of  the  red  solution  thus  produced  with  distilled  water  until  only 
a  faint  yellow  color  remains.  Divide  this  nearly  colorless  solu- 
tion into  four  parts.  To  one  add  2  or  3  c.c.  of  ferric  chloride,  to 
the  second,  about  twice  as  much  of  the  KCNS  originally  used, 
to  the  third,  add  one-half  its  volume  of  M/io  solution  of  KCl. 

Compare  portions  i  and  2  and  explain  how  this  experiment 
shows  the  law  of  chemical  equilibrium. 

Explain  also  how  it  illustrates  ionization  of  ferric  sulpho- 
cyanate  and  why  it  is  necessary  to  use  more  of  the  KCNS  than 
of  the  FeCls  solution  to  get  approximately  the  same  depth  of 
color. 

Now  compare  3  and  4  and  explain  how  these  solutions  show 
the  reversible  character  of  the  reaction  between  FeCls  and  KCNS. 
Do  portions  3  and  4  illustrate  law  of  mass  action? 

Peroxides. 

Exp.  17.  Prepare  a  solution  of  peroxide  of  hydrogen  as 
follows:  Add  to  10  or  15  grams  of  Ba02  enough  water  to  make 
a  paste  and  allow  to  stand  about  half  an  hour.  Then  add  20  or 
30  c.c.  of  a  ten  per  cent,  solution  of  H2SO4.  Stir  thoroughly  and 
after  five  minutes  filter  ofT  the  solution  and  test  for  H2O2.  (Test 
given  on  page  181.) 

The  half  hour  treatment  with  water  serves  to  hydrate  the 
Ba02  and  makes  the  action  of  the  acid  much  more  rapid. 

What  is  the  white  solid  remaining  on  the  filter  paper? 

Complete  Ba02  +  H2SO4  = 

Exp.  18.  Dissolve  peroxide  of  sodium  in  dilute  HCl  leaving 
the  reaction  faintly  acid.     Dissolve  also  a  little  peroxide  of 


372  EXPERIMENTS 

sodium  in  water  and  compare  the  bleaching  properties  of  the  two 
solutions. 

Exp.  19.  To  a  solution  of  HjOo  add  a  little  KI  solution,  then 
add  about  5  c.c.  of  chloroform.  Shake  well.  Set  aside  for  a 
few  moments  then  examine  and  explain  result. 

Exp.  20.  Dissolve  a  very  little  sodium  perborate,  NaBOa.- 
4H2O,  in  a  little  warm  water  and  test  the  solution  for  H2O2  with 
potassium  bichromate,  sulphuric  acid  and  ether  as  on  page  181. 

LABORATORY   WORK  IN    QUALITATIVE   ANALYSIS. 

During  the  study  of  qualitative  analysis  the  preliminary  work 
for  each  group,  which  may  consist  in  confirming  the  statements 
given  in  the  text  regarding  the  formation  of  precipitates  and 
properties  of  the  same,  should  be  carried  out  prior  to  the  analyses 
of  unknown  solutions.  In  addition  the  following  experiments 
may  be  used. 

Experiments  with  metals  of  Groups  I  and  II. 

Exp.  21.  Precipitate  a  little  silver  chloride  according  to  the 
following : 

AgNOa  +  NaCl  =  AgCl  +  NaNOs. 

Filter  and  allow  the  precipitate  to  become  nearly  dry.  Mix  a 
little  of  the  precipitate  with  powdered  charcoal,  and  heat  be- 
fore the  blowpipe  until  a  globule  of  metallic  silver  is  obtained. 

Exp.  22.  Mix  intimately  a  small  quantity  of  litharge  and 
powdered  charcoal.  Heat  in  a  blowpipe  flame  and  obtain  a 
particle  of  metallic  lead. 

Exp.  23.  In  a  solution  of  lead  (acetate  or  nitrate)  suspend 
a  strip  of  zinc.  Set  aside  for  several  hours  and  note  the  sepa- 
ration of  metallic  lead.     Write  the  reaction. 

Exp.  24.  Put  a  small  quantity  of  cinnabar  (HgS)  into  a 
small,  hard  glass  tube  open  at  both  ends.  Hold  the  tube,  slightly 
inclined,  in  a  strong  heat  of  the  Bunsen  flame;  then  examine  the 
sublimate  under  the  microscope.    What  becomes  of  the  sulphur? 


ALUMINIUM,  CHROMIUM  AND  IRON  ,    373 

Exp.  25.  Hold  a  strip  of  iron  or  steel  (knife  blade)  for  a 
few  seconds  in  a  solution  of  copper  sulphate.  Does  the  strip  of 
iron  dissolve?     If  so,  in  what  combination? 

Exp.  26.  In  an  open,  hard  glass  tube,  heat  strongly  a  mix- 
ture of  charcoal  and  copper  oxide.     Explain  the  change  of  color. 

Exp.  27.  To  a  very  small  piece  of  copper  foil  in  a  test-tube, 
add  a  little  ammonium  chloride  solution  and  allow  to  stand. 

Aluminium,  Chromium,  and  Iron. 

Exp.  28.  (a)  To  5  c.c.  of  dilute  alum  solution  containing  a 
little  NHiCl,  add  NH4OH  solution  and  heat. 

Note.  —  NH4CI  aids  in  the  complete  separation  of  the  Al2(OH)6. 

Write  reaction.  WiU  the  precipitate  dissolve  in  an  excess  of 
the  reagent? 

(b)    Repeat,  using  a  chromium  solution  in  place  of  the  alum.. 

Exp.  29.  Prepare  cobalt  aluminate  according  to  directions 
given  on  page  59.  This  should  result  in  a  line  blue  color;  two 
or  three  trials  may  be  necessary  to  produce  result. 

Exp.  30.  Dissolve  a  few  crystals  of  FeS04  in  water.  Filter, 
if  necessary,  and  to  a  portion  of  the  clear  solution  add  a  little 
ammonia  water.  To  another  portion  add  a  few  drops  of  HNO3 
and  boil  for  two  or  three  minutes.  Carefully  add  ammonia 
water  till  a  permanent  precipitate  is  obtained. 

To  a  solution  of  ferric  alum  add  a  Httle  ammonia.  What 
change  is  produced  by  the  HNO3  in  the  second  part  of  the 
experiment? 

FeS04  -f  NH4OH  =  ? 
3  H2SO4  H-  6  FeS04  +  2  HNO3  =  ? 
Fe2(S04)3  -f  NH4OH  =  ? 

Note.  —  The  addition  of  sulphuric  acid  is  not  necessary  to  the  oxidation  by 
HNO3-     It  simplifies  the  reaction^  as  other-nise  more  or  less  ferric  nitrate  is  formed. 

Exp.  31.  Make  a  little  fresh  solution  of  potassium  ferricy- 
anide,  also  a  solution  of  ferrous  sulphate;  to  the  latter  add  a 
little  H2SO4  and  a  piece  of  iron  wire.     After  hydrogen  ceases  to 


374  EXPERIMENTS 

be  evolved  make  the  following  tests,  completing  the  reaction  in 
each  case: 

FeS04  +  KaFeCye  =  ?  FcCle  +  KaFeCye  =  ? 

FeS04  +  KiFeCyo  =  ?  FcaCle  +  KjFeCye  =  ? 

FeS04  +  KCNS  =  ?  Fe.Clg  +  KCNS  -  ? 

Exp.  32.  To  a  solution  of  chrome  alum  add  a  little  NH4OH. 
Filter,  wash  the  precipitate  once  or  twice  and  allow  to  dry. 

Cr.  (504)3  +  NH4OH  =  ? 

To  this  dried  precipitate  add  a  little  dry  sodium  carbonate 
and  potassium  nitrate.  Mix  thoroughly,  transfer  to  a  porcelain 
crucible  and  heat  strongly  for  several  minutes,  cool  and  note  the 
color  of  the  fused  mass.  Dissolve  in  water,  acidify  with  acetic 
acid,  and  divide  the  solution  into  two  parts;  to  the  first  add  a  few 
drops  of  a  solution  of  Pb(N03)2  or  Pb(C2ll302)2,  and  to  the  second 
a  few  drops  of  BaClo. 

Cobalt,  Manganese,  Nickel,  afid  Zinc. 

Exp.  33.  Add  to  solutions  of  Co(N03)2,  MnS04,  Ni(N03)2, 
and  ZnS04  a  few  drops  of  (NH4)2S  solution. 

Note  color  of  precipitate  and  write  reaction  in  each  case. 

Exp.  34.  On  four  separate  filter  papers  collect  the  several 
precipitates  formed  in  Exp.  33.  Wash  once  with  HoO  and  make 
a  borax-bead  test  with  each  precipitate  as  shown  in  the  labora- 
tory demonstration.  To  each  precipitate  add,  on  the  paper, 
cold  dilute  HCl. 

Exp.  35.     (a)    To  a  solution  of  ZnS04  add  a  Httle  NH4OH. 
Will  the  precipitate  dissolve  in  excess  of  reagent? 

(&)    Repeat,  adding  NH4CI  before  using  the  NH4OH. 

(c)    Repeat  {a)  using  NaOH  in  place  of  NH4OH. 

Exp.  36.  Precipitate  a  little  MnS,  filter  and  wash.  Make 
red-lead  test  as  described  at  bottom  of  page  63. 

Exp.  37.     (a)   To  a  solution  of  Co(N03)2  in  a  test-tube,  add 


THE   ALKALINE  EARTHS  375 

a  drop  or  two  of  dilute  NH4OH.  Now  add  an  excess  of  NH4OH 
and  note  if  any  change  occurs. 

{b)    Repeat,  using  a  solution  of  NiS04. 

What  are  the  precipitates  formed? 

Exp.  38.  To  a  solution  of  zinc  salt  add  a  solution  of  NaaCOa. 
The  precipitate  is  a  basic  carbonate  of  zinc. 

Balance  the  equation 

ZnS04  +  NaoCOs  +  H2O  =  Zn5(OH)6(C03)2  +  Na2S04  +  CO.. 

Exp.  39.  Shake  in  a  test-tube  a  little  ZnO  and  water,  filter 
and  test  liltrate  for  Zn  as  in  Exp.  33. 

Repeat  using  ammonium  chloride  solution  instead  of  the 
water.     Inference. 

The  Alkaline  Earths. 

Exp.  40.  To  a  Kttle  clear  lime  water  add  a  few  drops  of 
ammonium  carbonate  solution. 

CaOsHo  +  (NH4)2C03  =  ? 

Will  an  excess  of  reagent  dissolve  this  precipitate?  If  CO2 
were  used  in  place  of  (NH4)2C03  would  the  solubility  of  the 
precipitate  be  the  same?     Why? 

Exp.  41.  Take  in  separate  test-tubes  about  5  c.c.  of  each 
of  the  following  dilute  solutions:  CaCl2,  BaCL,  Sr(N03)2,  and 
MgClo.  Add  to  each  i  or  2  c.c.  of  NHiCl  solution,  and  then  a 
little  (NH4)2C03  solution. 

Now  add  cautiously  to  each  tube,  containing  a  precipitate, 
dilute  acetic  acid  till  the  precipitates  are  all  dissolved.  To  each 
of  these  three  tubes  add  a  few  drops  of  K2Cr207  solution. 

Write  the  reactions.  Formulate  a  method  for  the  separation 
of  Ca,  Ba,  and  ]\Ig  from  a  mixture  containing  all  three. 

Exp.  42.  To  a,  solution  of  magnesium  chloride  add  a  little 
NH4OH  and  NH4CI  solution  and  lastly  some  sodium  phosphate. 

The  formula  for  the  precipitate  is  NH4MgP04.  Complete  the 
reaction. 

MgCl2  +  Na2HP04  +  NH4OH  = 


376  EXPERIMENTS 

Exp.  43.  To  each  of  the  four  solutions  used  in  Exp.  41  add 
a  little  dilute  H0SO4. 

Which  of  the  four  metals  forms  the  least  soluble  sulphate? 

Which  the  most  soluble? 

Exp.  44.  To  a  solution  of  Sr(N03)2  add  a  solution  of  CaS04 
and  allow  to  stand. 

Exp.  45.  To  a  solution  of  a  calcium  salt  add  some  ammo- 
nium oxalate  solution.     Write  reaction. 

Exp.  46.  In  a  watch  glass  place  a  few  drops  of  lime  water, 
in  another  place  some  baryta  water.  Set  the  two  glasses  aside 
for  a  while  and  explain  any  change  that  takes  place. 

Exp.  47.  ]\Iake  flame  tests  with  solutions  of  barium,  stron- 
tium and  calcium. 

The  Alkali  Metals. 

Exp.  48.  In  10  or  15  c.c.  of  water  contained  in  a  porcelain 
dish,  dissolve  a  small  piece  of  metaUic  potassium. 

Stand  well  away  from  the  dish  as  the  reaction  may  result  in 
spattering  hot  water  or  hot  metal. 

Test  resulting  solution  with  red  Htmus  paper.*  Write  reac- 
tion. 

Exp.  49.  Take  a  Httle  strong  solution  of  carbonate  of  soda 
(about  20%  of  crystalHzed  salt),  heat  nearly  to  boiling  in  a 
porcelain  dish,  then  add  about  half  as  much  milk  of  lime  (made 
of  one  part  Ca(0H)2  to  four  parts  water).  Continue  the  boil- 
ing for  several  minutes,  then  allow  to  settle.  Decant  the  clear 
liquid. 

Test  the  Uquid  with  various  indicators.  Is  it  acid  or  alka- 
Hne? 

To  a  small  portion  of  it  add  a  few  drops  of  HCl.  Does  it 
effervesce?  Test  in  a  similar  manner  the  carbonate  of  soda 
solution, 

NasCOa  +  CaHsOs  =  ? 

*  Blue  paper  vm.y  be  reddened  by  leaving  it  a  few  hours  in  a  wide-mouth 
bottle  after  wetting  the  under  side  of  the  stopper  with,  a  drop  or  two  of  acetic  acid 


THE  ALKALI  METALS  377 

Which  of  these  two  compounds  used  is  a  base? 

Which  an  alkali? 

Exp.  50.     In  separate  test-tubes  heat  the  following  mixtures: 

1.  Solution  of  NH4CI  and  solution  of  NaOH. 

2.  Solution  of  (NH4)2S04  and  solution  of  KOH. 

3.  Dry  NH4CI  and  dry  CaOaHo. 

In  each  case  note  the  odor  of  the  gas  evolved  and  test  the 
VAPOR  with  moistened  red  litmus  paper  and  write  the  reaction. 

Exp.  51.  Take  three  test-tubes  and  into  one  put  about 
5  c.c.  of  a  dilute  solution  NaCl;  into  the  second,  KCl;  and  into 
the  third,  NH4CI;  then  to  each  add  a  few  drops  of  platinic 
chloride  solution  and  allow  to  stand  till  the  next  exercise. 

Exp.  52.  Make  flame  tests  according  to  directions  given  in 
the  lecture  room,  with  salts  of  sodium,  potassium,  and  lithium. 

Exp.  53.  Place  in  an  ignition  tube  one  or  two  grams  of 
potassium  tartrate  and  heat  till  no  further  change  takes  place. 
Cool  and  dissolve  in  water.  Test  a  portion  of  the  resulting 
solution  with  a  few  drops  of  HCl.  In  like  manner  test  the 
original  tartrate. 

Note.  —  In  general,  the  ignition  of  salts  of  organic  acids  results  in  the  for- 
mation of  carbonates. 

•  Exp.  54.     Make  a  spectroscopic  examination  of  solutions  of 
Na,  K,  Li,  Ba,  Sr,  and  Ca,  and  describe  the  bands  observed. 

Note.  —  This  experiment  is  only  to  be  performed  under  the  direction  of  an 
instructor.  Opportunity  will  be  given  for  this  experiment  during  the  next  exer- 
cise if  necessary. 

EXPERIMENTS   FOR   CHAPTER  XI. 

Exp.  55.  Heat  in  forceps  or  on  triangle  a  very  small  piece 
of  each  of  the  following  metals,  allowing  each  to  fall  as  it  melts 
onto  a  smooth  cold  slab  (cement  floor  will  do).  Return  melted 
metals  to  office  for  credit. 

Ni-F^Cu-Mg-Zn-Cd-Bi-Sn. 


378  EXPERIMENTS 

Study  table  of  melting-points  and  write  your  conclusions  regard- 
ing the  temperature  of  the  Bunsen  flame. 

Exp.  56.  Fill  each  of  three  test-tubes  half  full  of  a  solution  of 
CUSO4.  Suspend  in  the  first  a  knife  blade;  in  the  second,  a 
strip  of  clean  metallic  zinc;  in  the  third,  a  strip  of  magnesium 
ribbon.     Write  reactions. 

Exp.  57.  Warm  gently  in  a  test-tube  a  little  Mn02  and  HCl. 
Write  reactions.  Repeat  with  PbO-i  and  HCl;  with  PbO  and 
HCl.     Explain  differences  in  action  of  the  metallic  oxides. 

EXPERIMENTS   FOR   CHAPTERS   XH-XIV. 

During  the  study  of  Chapters  XH-XIV  inclusive,  the 
student  will  be  required  to  make  qualitative  analyses  of  several 
commercial  alloys,  dental  cements,  etc.  He  will  also  have  to 
prepare  and  test  carefully  six  alloys,  the  formulae  for  which  will 
be  given  on  a  mimeograph  sheet  similar  to  that  represented 
on  page  379. 

The  properties  of  the  various  alloys  are  to  be  carefully  com- 
pared and  it  is  often  desirable  for  two  or  more  students  to  vary 
a  given  formula  in  some  one  particular  and  note  the  result  of 
such  a  variation  upon  the  properties  of  the  amalgam  obtained. 


THE  ALKALI   METALS 
ALLOYS. 


379 


Date. 


Desk  No Name  . 


No.  I. 

No.  2. 

No.  3- 

No.  4. 

No.  S- 

No.  6. 

Gold 

Silver 

1 8 

6o 

55 

Tin 

3 

•    I 

6S 

40 

37 

Copper 

4 

Zinc 

4 

Lead 

5 

2 

Antimony 

17 

Bismuth 

8 

4 

Cadmium 

I 

Nos.  I  and  2  contain  lead  and  must  not  under  any  circumstances  be  made 
in  the  graphite  crucible  which  you  intend  to  use  for  silver-tin  alloj-s.  These 
are  solders  or  fusible  metals.  IMake  8  to  10  grams  and  determine  melting-point 
of  each. 

No.  3  is  a  ver\'  low  grade  dental  alloy.  IMake  10  grams  and  test  for  expansion, 
discoloration,  and  crushing  strength. 

Nos.  4  and  5  are  better  grade  alloys.  j\Iake  10  or  12  grams  of  each.  Hand 
one  in  as  sample  of  work;  test  the  other,  annealed  and  imannealed,  as  No.  3  was 
tested. 

No.  6,  your  own  formula.  ]\Iake  15  to  20  grams.  Make  complete  tests 
and  also  return  sample.  Return  all  remaining  portions  of  alloys  ^4th  desk  number 
and  composition  of  the  alloy  plainly  written  on  envelopes  furnished,  in  order  to 
obtain  proper  credit  for  the  work. 


380  EXPERIMENTS 

CHAPTER  XV. 

As  part  of  the  work  in  studying  dental  cements  the  student 
is  expected  to  make  a  mixture  of  pure  zinc  oxide  and  sirupy 
phosphoric  acid;  then  to  study  the  modification  of  the  properties 
of  the  resulting  cement  by  various  additions  of  insoluble  phos- 
phates and  magnesium  oxide  to  the  acid  or  powder.  He  is  also 
expected  to  make  qualitative  analyses  of  two  commercial  cements 
one  of  which  shall  be  a  copper  cement. 

CHAPTER    XVn. 

Standard  solutions  are  prepared  illustrating  volumetric  proc- 
esses by  neutralization,  oxidation  and  precipitation.  Numer- 
ous unknown  quantitative  solutions  are  given  each  student  for 
practice. 

CHAPTERS   XIX  AND   XX. 

In  the  study  of  substances  commonly  used  in  dental  prepara- 
tions the  simpler  tests  are  regarded  as  important;  these  have 
been  included  in  the  text.  If  time  permits  the  analysis  of  a  few 
unknown  anesthetics,  mouth  washes  and  powders  wiU  aid 
materially  in  fixing  the  composition  of  this  class  of  substances  in 
the  student's  mind. 

If  material  is  available  the  analysis  of  various  forms  of  tartar 
is  especially  instructive.  It  will  be  necessary  to  use  the  micro- 
chemical  methods  suggested  in  Chapter  XVIII  for  this  work. 

ORGANIC   CHEMISTRY. 

Experiments  witJi  Carbon  and  Hydrocarbons. 

Exp.  58.  Carbon  as  a  decolorizing  agent.  To  25  or  30  c.c. 
of  a  dilute  solution  of  aniline  color,  contained  in  a  small  beaker, 
add  a  teaspoonful  of  bone  charcoal.  Heat  to  the  boiling-point, 
rotate  or  stir  thoroughly  for  a  few  minutes,  and  filter. 

Exp.  59.     Absorption  of  metalhc  salts.     To  25  c.c.  of  solu- 


EXPERIMENTS   WITH   CARBOX   AXD   HYDROCARBONS-    38 1 


tion  of  lead  acetate  of  such  strength  that  H2S  water  gives  marked 
color  but  no  precipitate,  add  a  teaspoonful  of  bone  charcoal  and 
treat  as  in  preceding  experiment.  Test  the  filtrate  with  H2S 
water  and  note  whether  lead  has  been  removed. 

Exp.  60.  Perform  an  experiment  with  a  \iew  to  determin- 
ing whether  bone  charcoal  will  absorb  HoS  from  H2S  water. 

Exp.  61.  Repeat  either  of  the  three  immediately  preceding 
experiments,  using  wood  charcoal  in  place  of  bone  charcoal. 
Does  the  wood  charcoal  work  as  well  as  the  bone  charcoal  in 
the  absorption  of  color  or  other  substances?  How  does  bone 
charcoal  differ  in  composition  from  wood  charcoal? 

Exp.  62.  Arrange  apparatus  as  shown  in  Fig.  34.  To  the 
boiling  flask  {B)  pro^dded  with  a  thermometer  registering  200°  C. 


Fig.  34. 

connect  a  beaker  condenser,  C,  immersed  in  ice  water.  In  this 
apparatus  distil  slowly  25  c.c.  of  crude  petroleum  until  at  least 
four  fractional  products  are  obtained,  with  boiling  points  differing 
by  at  least  15°.  Compare  the  physical  properties  of  the  distil- 
lates thus  obtained. 

Exp.    63.     Charge   an  ignition   tube  with   dry  "marsh-gas 
mixture,"  found  on  side  shelf  (consisting  of  NaC2H302,  NaOH, 


382  EXPERIMENTS 

and  Ca02H2).     Fit  with  a  delivery  tube  and  collect  two  small 
bottles  of  the  gas  over  water. 

NaCsHsOo  +  NaOH  =  CH4  +  NasCOg. 

Test  the  inflammability  of  this  gas.     Notice  the  odor. 

Exp.  64.  Mix  carefully  in  a  test-tube  2  c.c.  of  alcohol  and 
8  c.c.  of  strong  sulphuric  acid.  Heat  gently  and  notice  odor  of 
gas.  Fit  a  bent  glass  tube  to  the  test-tube  and  collect  over 
water  a  test-tube  full  of  the  gas.  To  this  apply  a  flame.  Note 
the  color  of  the  burning  gas. 

C2H5OH  -  HoO  =  C2H4. 

Exp.  65.  Collect  a  test-tube  full  of  ethylene  (Exp.  64),  add 
a  few  c.c.  of  dilute  permanganate  solution  and  shake.  Then 
repeat,  using  Marsh  gas  in  place  of  the  ethylene  (test  for  un- 
saturated hydrocarbons). 

Exp.  66.  Shake  together,  in  separate  test-tubes,  small 
quantities  of  petroleum  and  sulphuric  acid  in  one  tube,  and 
petroleum  and  nitric  acid  in  the  other.  If  no  action  results,  mix 
contents  of  the  two  tubes  and  shake  again.  Explain  any  change 
or  absence  of  change  which  may  be  apparent. 

Exp.  67.  In  a  small  generator  (see  model)  place  a  few  small 
pieces  of  calcium  carbide  (CaC2),  add  strong  alcohol  through  the 
funnel  tube  till  the  lower  end  of  the  tube  is  "sealed."  Now 
add  very  slowly  a  little  water  till  a  brisk  evolution  of  gas  is 
obtained.  Collect  over  water  two  or  three  test-tubes  full  of  the 
gas.     (Acetylene.) 

Test  with  a  Hghted  splinter.  Note  odor  of  gas  cautiously, 
as  it  is  poisonous  when  inhaled  in  quantity. 

CaCo  +  2  H2O  =  Ca(0H)2  -f  C2H2. 

Exp.  68.  Conduct  a  little  of  the  acetylene  gas  into  an 
ammoniacal  cuprous  chloride  solution.*  What  is  the  red  pre- 
cipitate? 

*  See  appendix  for  preparation  of  reagent.  This  test  is  characteristic  of  the 
triple-bonded  hydrocarbons. 


EXPERIMENTS  WITH  CARBON  AND  HYDROCARBONS      383 

Exp.  69.  If  the  evolution  of  gas  (Exp.  68)  has  not  been 
interrupted  the  delivery  tube  may  be  replaced  by  a  short  tube 
drawn  out  to  a  fine  point  and  the  gas  ignited.  Note  color  of 
flame.     If  it  smokes  badly,  explain  the  reason  for  it. 

Experiments  mith  the  Halogen  Derivatives  of  the  Hydrocarbons. 

Exp.  70.  Place  in  a  test-tube  a  Httle  bleaching-powder, 
cover  with  strong  alcohol  and  heat  the  mixture  to  boihng. 
Notice  carefully  the  odor  of  the  vapor  produced  and  compare 
with  a  little  chloroform  (CHCI3)  from  side  shelf. 

4  C2H5OH  +  8  Ca(C10)2  =  2  CHCI3  +  3  Ca(CH02)2 

(Formate  of  Ca) 

+  5  CaCl2  +  8  H2O. 

Exp.  71.  Heat  i  c.c.  of  chloroform  with  about  5  c.c.  of 
one  per  cent  NaOH.  Test  a  portion  of  the  resulting  solution 
for  inorganic  chlorides.  Distil  the  remainder  of  the  solution  and 
test  the  distillate,  collected  in  a  test-tube,  with  litmus  paper. 

Exp.  72.  Place  in  a  test-tube  about  i  gram  of  crystallized 
carbonate  of  sodium,  about  half  as  much  iodine  and  i  or  2  c.c.  of 
alcohol.  Now  add  10  or  15  c.c.  of  H2O  and  keep  the  mixture 
at  moderate  heat  (not  boiling)  till  the  color  of  the  iodine  is  dis- 
charged. Allow  to  cool;  collect  on  a  small  filter  paper  some  of 
the  yellow  crystals  which  have  been  formed  and  examine  under 
the  microscope.  What  are  the  crystals?  Explain  their  rela- 
tion to  marsh-gas. 

Exp.  73.  Prepare  ethyl  bromide  from  alcohol,  potassium 
bromide  and  sulphuric  acid  as  follows:  Using  the  apparatus 
suggested  for  experiment  62,  place  in  the  distilling  flask  about 
30  c.c.  of  50%  alcohol.  Add  slowly  with  constant  agitation 
30  c.c.  of  strong  sulphuric  acid.'  Cool  thoroughly,  then  add  30 
grams  of  powdered  potassium  bromide.  Distil  carefully  until 
condenser  is  nearly  full  of  distillate.  Pour  about  a  quarter  of 
the  product  into  excess  of  water.     Shake  well  to  wash  the  ethyl 


384  EXPERIMENTS 

bromide.  Remove  from  the  wash  water  by  means  of  a  pipette 
and  dissolve  in  a  little  alcohol.  Test  this  alcoholic  solution  for 
bromine  with  alcoholic  silver  nitrate. 

To  another  portion  of  the  ethyl  bromide  add  5  to  10  c.c.  of 
alcoholic  potassium  hydroxide  (5%  in  absolute  alcohol).  Boil 
for  a  minute  or  two,  dilute  with  water  and  make  the  usual 
qualitative  test  for  bromides. 

Write  reactions. 

Ethyl  bromide  may  also  be  prepared  by  distilling  a  mixture 
of  one  part  of  alcohol  and  five  parts  of  strong  hydrobromic  acid. 

Exp.  74.  Cover  one  or  two  small  pieces  of  calcium  carbide, 
in  a  small  porcelain  dish,  with  a  mixture  of  three  parts  water  and 
one  part  alcohol.  While  the  gas  is  being  evolved  hold  over  the 
mixture  a  test-tube  full  of  chlorine. 

Experiments  with  Alcohols.     {Chap.  XXII.) 

Exp.  75.  The  detection  of  water  in  alcohol.  Prepare  a 
little  anhydrous  copper  sulphate  by  heating  a  few  crystals  of 
CUSO4  on  a  crucible  cover  until  the  water  is  driven  off  and  a 
nearly  white  powder  results.  If  this  white  powder  is  added 
to  half  a  test-tube  full  of  alcohol,  the  absorption  of  water,  if 
present,  will  result  in  reforming  the  crystallized  salt  and  a  con- 
sequent production  of  blue  color. 

Exp.  76.  Water  may  be  separated  from  alcohol  by  saturat- 
ing with  potassium  carbonate.  To  demonstrate  this,  take  a 
mixture  of  alcohol  and  water,  containing  fifteen  or  twenty  per 
cent  of  alcohol,  and  add  solid  potassium  carbonate  until  the  salt 
will  no  longer  dissolve.  Agitate  and  allow  to  stand.  Two  layers 
will  form,  one  consisting  of  alcohol,  the  other  of  the  water  solu- 
tion of  K2CO3. 

Exp.  77.  To  about  75  c.c.  of  a  10%  glucose  solution  add 
a  little  yeast  and  allow  to  stand  for  twenty-four  hours  at  a 
temperature  of  about  37°  C;  then  distil  by  means  of  gentle 
heat  10  or  15  c.c,  and  test  distillate  for  alcohol  by  iodoform  test, 


ALDEHYDES  AND  KETONES  385 

as  given  on  page  383,  Exp.  72.  The  production  of  CO2  may 
also  be  demonstrated  if  the  gases  evolved  during  the  fermentation 
are  passed  into  clear  lime  water: 

CeHioOe  =  2  C0H5OH  +  2  COo. 

Exp.  78.  A  test  for  methyl  alcohol.  This  test  is  applicable 
only  to  slight  traces  of  methyl  alcohol  and  may  be  made  with 
a  one  to  two  per  cent  solution  or  with  the  first  cubic  centimeter 
of  distillate  from  the  substance  suspected  of  containing  methyl 
alcohol.  Place  2  or  3  c.c.  of  very  dilute  methyl  alcohol  in  a 
test-tube,  heat  a  spiral  of  copper  wire  to  white  heat  in  a  Bunsen 
flame  and  plunge  immediately  into  the  solution  to  be  tested. 
Cool  the  contents  of  the  tube  by  immersion  in  freezing  mixture 
or  ice  water,  and  repeat  the  treatment  with  the  hot  copper  wire. 
Cool  again,  and  a  third  time  introduce  the  hot  copper  wire. 
The  copper  spiral  can  be  made  by  winding  copper  wire  around  a 
lead  pencil,  and  should  be  of  such  a  length  that  it  is  not  wholly 
covered  by  the  liquid  in  the  tube. 

This  process  serves  to  oxidize  a  portion  of  the  alcohol  to 
aldehyde.  Now  add  to  the  solution  which  is  being  tested  a  few 
drops  of  a  1/2%  water  solution  of  resorcinol  and  underlay  the 
mixture  with  strong  sulphuric  acid.  A  violet  ring  will  indicate 
the  presence  of  methyl  alcohol.  The  higher  alcohols  will  give 
red  or  brown  rings  when  similarly  treated. 

Exp.  79.  Repeat  experiment  78,  using  ethyl  alcohol  in  place 
of  methyl  alcohol. 

Exp.  80.  In  5  or  10  c.c.  of  absolute  alcohol  dissolve  1/4  to 
1/2  gram  of  metallic  sodium.     Test  the  gas  given  off. 

Write  reaction.     Save  the  product. 

Exp.  81.  Repeat  Exp.  57,  using  allyl  alcohol  instead  of 
ordinary  aicohol. 

Experiments  with  Aldehydes  and  Ketones.     {Chap.  XXII.) 

Exp.  82.  Mix  about  i  c.c.  of  a  very  dilute  solution  of  for- 
maldehyde with  four  or  five  times  its  volume  of  milk  in  a  test- 


386  EXPERIMENTS 

tube.  Keep  at  a  temperature  of  40  to  50°  C.  for  half  an  hour, 
then  carefully  underlay  the  mixture  with  commercial  sulphuric 
acid  of  a  specific  gravity  of  1.80.  At  the  point  of  contact  of  the 
two  layers  of  liquid  a  violet-colored  ring  indicates  the  presence 
of  formaldehyde.  It  is  necessary  that  time  be  allowed  for  the 
casein  of  the  milk  to  unite  with  the  formaldehyde,  also  that  the 
sulphuric  acid  should  contain  a  trace  of  iron ;  this  the  commercial 
acid  usually  does.  It  is  undesirable  that  the  acid  should  be 
stronger  than  of  1.80  specific  gravity;  for,  if  it  is,  a  reddish-brown 
ring  may  be  formed,  due  to  partial  carbonization  of  the  casein. 

Exp.  83.  To  a  very  dilute  solution  of  formaldehyde  add  a 
few  drops  of  1/2%  resorcinol  solution  and  underlay  the  mixture 
with  H2SO4  as  in  Exp.  78.  The  appearance  of  a  violet  ring  will 
constitute  a  test  for  formaldehyde. 

Exp.  84.  To  about  5  c.c.  of  a  strong  aqueous  solution  of 
potassium  dichromate  add  a  little  sulphuric  acid,  then  a  few 
cubic  centimeters  of  alcohol,  and  notice  the  odor  of  acetaldehyde 
produced  by  oxidation  of  the  alcohol.  Note  also  the  reduction 
of  the  dichromate  to  Cr2(S04)3,  as  follows: 

KaCraOT  +  4  H2SO4  +  3  C2H5OH  = 

K2SO4  +  Cr2(S04)3  +  3  C2H4O  +  7  H2O. 

Exp.  85.  Test  dilute  solutions  of  acetone,  formic  and  acetic 
aldehydes  by  ToUen's  test  for  aldehyde  as  follows:  Into  a  clean 
test-tube  which  has  been  rinsed  with  NaOH  solution,  place  5  c.c. 
of  ToUen's  reagent,  add  10  c.c.  of  solution  to  be  tested,  shake; 
the  silver  is  reduced,  forming  a  metalHc  mirror  on  the  inner  sur- 
face of  the  tube. 

To*  make  ToUen's  reagent,  dissolve  three  grams  of  silver 
nitrate  in  30  c.c.  ammonia  water  and  add  3  c.c.  of  solution  of 
sodium  hydroxide. 

Exp.  86.     Prepare  acrolein  in  each  of  the  following  ways: 

ist:   From  glycerol  according  to  the  test  given  on  page  179. 

2nd:  Oxidize  one  or  two  drops  of  aUyl  alcohol  with  potassium 


EXPERIMENTS   WITH  ACETONE  '  387 

bichromate  and  H2SO4,  similar  to  the  oxidation  of  ethyl  alcohol 
in  Exp.  84. 

Exp.  87.  To  about  5  c.c.  of  an  aqueous  solution  of  chloral 
hydrate  add  a  few  cubic  centimeters  of  strong  NaOH  solution 
and  boil.     Note  odor  of  chloroform. 

Exp.  88.  Isobenzonitril  test  for  chloral  or  chloroform: 
Place  a  few  drops  of  a  dilute  chloral  hydrate  solution  (or  a  small 
drop  of  chloroform)  in  a  test-tube,  add  5  c.c.  of  an  alcohohc 
solution  of  alkaU  hydrate*  (NaOH  or  KOH)  and  one  drop  only 
of  fresh  aniline  oil.  Heat  tiU  the  mixture  just  begins  to  boil 
and  note  the  odor  of  the  nitril. 

Exp.  89,  Test  2  or  3  c.c.  of  an  aqueous  solution  of  aldehyde 
with  an  equal  volume  of  Schiff's  reagent. 

Experiments  with  Acetone. 

Exp.  90.  Preparation  of  acetone:  Heat  a  few  grams  of 
dried  calcium  acetate  in  an  ignition  tube,  collect  the  distillate, 
which  consists  of  an  impure  acetone.  If  this  is  mixed  with  a 
little  water  and  filtered,  part  of  the  impurities  may  be  removed, 
and  the  filtrate  tested  for  acetone  by  the  following  experiment. 

Exp.  91.  Dilute  the  filtrate  from  the  last  experiment  with 
distilled  water;  add  a  crystal  of  sodium  nitroprusside.  After 
the  crystal  is  dissolved,  add  a  few  drops  of  acetic  acid,  and  then 
an  excess  of  ammonia  water.  A  violet  or  purple  color  indicates 
the  presence  of  acetone.  Using  a  dilute  solution  of  acetone  in 
place  of  the  alcohol  in  experiment  72,  on  page  383,  produce  iodo- 
form crystals  by  similar  reaction  with  iodine  and  sodium  or  po- 
tassium carbonate. 

Exp.  92.  Acetone  may  be  dissolved  or  mixed  with  water  in 
all  proportions;  but,  upon  saturating  the  water  with  KOH, 
the  acetone  will  form  a  separate  layer  which  may  be  drawn  off  as 
in  the  separation  of  alcohol  in  experiment  76,  page  384. 

*  If  alcoholic  potash  or  soda  is  not  at  hand,  the  test  may  be  performed  with 
5  c.c.  of  alcohol  and  i  or  2  c.c.  of  a  40%  aqueous  solution  of  NaOH. 


388  EXPERIMENTS 

Experiments  with  Ethers. 

Exp.  93.  Into  a  large  test-tube  put  a  little  alcohol  and  about 
half  its  volume  of  strong  H2SO4.  Warm  gently  and  notice  the 
odor. 

Ether  is  formed  by  two  reactions.  First,  C2H5OH  +  H2SO4 
=  C2H5HSO4  +  HoO.  Then  the  ethyl-hydrogen  sulphate 
(C2H5HSO4)  is  acted  upon  by  a  second  molecule  of  H2SO4,  as 
follows:  C2H5HSO4  +  CoHaOH  =  (C2H5)20  -f-  H2SO4. 

Exp.  94.  The  production  of  compound  ethers  may  be  dem- 
onstrated by  the  test  for  acetic  acid  forming  ethyl  acetate, 
page  100,  or  by  the  following  experiment  used  to  detect  butyric 
acid  in  gastric  contents: 

Exp.  95.  Mix  in  a  test-tube  5  c.c.  of  a  dilute  (1/2%)  solu- 
tion of  butyric  acid  with  an  equal  volume  of  strong  H2SO4  and 
as  much  strong  alcohol.  Heat  gently  and  note  the  odor  of 
ethylbutyrate  (pineapples) . 

Exp.  96.  Mix  carefully  equal  portions  of  cold  alcohol  and 
strong  H2SO4,  about  10  c.c.  of  each.  Then  pour  the  mixture  into 
about  200  c.c.  of  water  and  add  in  small  portions  barium  carbon- 
ate in  excess.  Allow  to  stand  a  little,  filter  and  test  filtrate  for 
barium.  Concentrate  the  solution  of  barium  ethyl  sulphate 
thus  obtained  over  a  water  bath  to  about  half  its  volume.  Then 
mix  about  10  c.c.  with  2  or  3  c.c.  of  dilute  HCl  and  distil.  Test 
a  portion  of  the  distillate  for  acid  and  for  SO4.  Warm  the 
remainder  with  an  equal  volume  of  alcohol  and  note  if  ether  is 
produced. 

Exp.  97.  The  action  of  fixed  alkalies  on  compound  ethers 
is  known  as  "saponification."  It  may  be  illustrated  by  heating 
10  c.c.  of  ethyl  acetate  with  80  c.c.  of  a  10%  NaOH  solution  for 
30  to  40  minutes,  when  the  odor  of  ethyl  acetate  should  be 
destroyed.  The  flask  should  be  connected  with  a  reflux  con- 
denser and  the  heat  applied  by  immersing  the  flask  in  boiling 
water.     Write  reaction. 


EXPERIMENTS  WITH  ORGANIC  ACIDS  389 

Experiments  with  Organic  Acids  (C„H2„02). 

Exp.  98.  Introduce  into  a  small  flask  (250  c.c.  capacity) 
about  30  c.c.  of  anhydrous  glycerin  and  an  equal  weight  of 
oxalic  acid  crystals.  Boil  for  several  minutes;  CO2  is  given 
off  and  a  compound  formed  between  the  acid  and  glycerin; 
then,  upon  addition  of  more  acid  and  continued  heating,  formic 
acid  may  be  distilled.  Collect  about  10  c.c.  of  distillate;  test 
reaction  with  litmus-paper.  Make  silver-mirror  test,  described 
on  page  386,  Exp.  85.  The  silver  solution  will  be  reduced,  but 
difficulty  will  be  experienced  in  obtaining  the  mirror. 

Exp.  99.  To  5  c.c.  of  formic  acid  solution  add  2  or  3  c.c.  of 
dilute  H2SO4  (1-5)  and  a  Httle  potassium  permanganate  solu- 
tion; heat  the  mixture  and  conduct  the  gas  evolved  into  a  tube 
containing  lime  water. 

Exp.  100.  From  a  mixture  of  formic  acid,  alcohol,  and  sul- 
phuric acid,  ethyl  formate  may  be  evolved  in  a  manner  similar 
to  that  in  the  production  of  ethyl  acetate  (page  100).  Compare 
the  odors  of  these  two  ethers. 

Exp.  loi.  To  a  dilute  aqueous  solution  of  acetone  add 
potassium  permanganate  slowly  until  the  mixture  is  perma- 
nently colored  pink;  filter,  add  dilute  sulphuric  acid  and  distil 
until  I  or  2  c.c.  of  distillate  are  obtained.  This  may  be  tested 
for  acetic  acid  by  litmus  paper  and  ferric  chloride. 

Exp.  102.  To  a  dilute  solution  of  ferric  chloride  add  a  Httle 
acetic  acid;  divide  the  solution  into  two  parts;  to  one  add  mer- 
curic chloride  and  to  the  other  HCl,  and  note  results. 

Exp.  103.  Repeat  Exp.  102,  usmg  diacetic  acid  in  place  of 
acetic. 

Exp.  104.  Repeat  Exp.  102,  using  meconic  acid*  in  place  of 
acetic. 

Compare  results  of  these  three  experiments  and  save  record 
for  future  use  in  the  study  of  saliva. 

*  Laudanum  diluted  with  water  till  color  is  light  brown  may  be  used. 


390  EXPERIMENTS 

Exp.  105.  In  a  small  flask  saponify  a  little  butter  by  heating 
with  alcoholic  potash  over  a  steam  bath  till  mixture  is  dry. 
Dissolve  in  water,  add  dilute  H2SO4,  and  distil  off  a  portion  of 
the  butyric  acid.  Record  whatever  can  be  learned  from  this 
experiment  regarding  the  physical  properties  of  the  butyric  acid. 

Exp.  106.  In  separate  test-tubes  take  about  5  c.c.  of  solu- 
tions of  stearic  and  oleic  acids  in  carbon  tetrachloride.  Add  to 
each  about  i  c.c.  of  a  one-tenth  per  cent  solution  of  iodine  also 
in  carbon  tetrachloride,  allow  to  stand  for  some  time,  and 
explain  Jully  the  difference  in  action  exhibited  by  the  two  fatty 
acids. 

Experiments  with  Organic  Acids  not  of  the  CJHirPi  Series. 

Exp.  107.  To  a  dilute  solution  of  permanganate  of  potassium 
'add  a  few  drops  of  sulphuric  acid  and  heat  nearly  to  boiling. 
Note  if  any  change  takes  place.  Now  add  a  few  crystals  of  ox- 
alic acid  and  watch  carefully.     Explain  the  use  of  sulphuric  acid. 

Exp.  108.  In  separate  test-tubes,  insoluble  oxalates  may  be 
produced  by  adding  a  solution  of  ammonium  oxalate  to  a  solu- 
tion of  (a)  calcium  chloride,  {h)  silver  nitrate,  {c)  zinc  sulphate, 
{d)  copper  sulphate,  (e)  lead  nitrate. 

Exp.  109.  Place  in  an  ignition  tube,  fitted  with  delivery  tube 
to  collect  evolved  gas  in  test-tube,  about  3  grams  of  dry  calcium 
oxalate.  Heat  strongly  and  test  gas  evolved  with  lighted  match 
or  spHnter.  After  ignition  tube  has  become  cold  add  dilute 
H2SO4  and  pass  gas  evolved  into  lime  water. 

Exp.  no.  Dissolve  about  3  grams  of  dry  oxalic  acid  (100°  C.) 
in  a  test-tube  half  full  of  methyl  alcohol.  It  will  probably  be 
necessary  to  boil  the  mixture  before  solution  is  complete  and 
great  care  must  be  used  to  avoid  burning  of  the  alcohol.  The 
use  of  a  water  bath  is  recommended.  As  the  hot  mixture  cools, 
dimethyloxalate  will  crystallize  out. 

Separate  sufificient  of  the  crystals  to  obtain  melting-point, 
wh-ich  should  be  about  54°  C. 


EXPERIMENTS   WITH   CYANOGEN   COMPOUNDS     .       39 1 

Exp.  III.  The  ester  prepared  in  above  experiment  may  be 
dissolved  in  alcohol  and  upon  addition  of  NH4OH  will  give  a 
precipitate  of  oxamide. 

Exp.  112.  Take  a  test-tube  half  full  of  calcium  chloride 
(10%),  make  strongly  alkaline  with  JSTHiOH  and  pass  CO2  into 
the  mixture  for  several  minutes.  A  solution  of  calcium  carbon- 
ate will  result. 

Write  reaction,  CaCl2  +  2  CO2  +  4  NH4OH  =  ?.  Heat  the 
solution  of  calcium  carbonate  just  produced  till  a  precipitate  of 
CaCOa  is  produced. 

Write  reactions  showing  the  formation  of  CaH2 (003)2  and  the 
precipitation  of  CaCOa  from  the  acid  salt. 

Exp.  113.  To  1/3  test-tube  of  cider  vinegar  add  a  few  cubic 
centimeters  of  basic  acetate  of  lead  solution;  a  bulky  precipitate 
of  lead  malate  separates. 

Exp.  114.  Dilute  a  few  drops  of  neutral  ferric  chloride  solu- 
tion until  no  color  is  discernible,  then  to  10  c.c.  of  this  dilution 
add  4  to  5  drops  of  1/2%  solution  of  lactic  acid.  A  greenish- 
yellow  color  constitutes  a  positive  test. 

In  practical  application  of  this  test,  it  needs  further  con- 
firmation by  boiling  the  unknown  solution  with  a  drop  or  two 
of  HCl  and  then  extracting  with  ether.  Evaporate  the  ether, 
take  up  the  residue  in  2  or  3  c.c.  of  water  and  repeat  the  test 
as  given  above.  If  the  yellow  color  persists,  it  is  due  to  lactic 
acid. 

Experiments  with  Cyanogen  Compounds.     (Chap.  XXV.) 

Exp.  115.  In  a  large  test-tube  dissolve  one  half  gram  or  less 
of  potassium  ferrocyanide  in  about  4  c.c.  of  water.  Add  a  little 
H2SO4  and  boil,  conducting  the  gas  evolved  into  a  beaker  con- 
denser (Fig.  35)  by  means  of  a  bent  glass  tube.  Note  the  odor 
of  this  dilute  ^solution.  (Do  not  smell  of  the  contents  of  generat- 
ing tube,  as  the  strong  acid  is  intensely  poisonous.)  Write 
reaction. 


392  EXPERIMENTS 

Exp.  ii6.  To  one  half  of  the  dilute  hydrocyanic  acid 
prepared  in  the  previous  experiment  add  a  drop  or  two  of 
AgNOs  solution  with  a  little  HNO3.  After  the  precipitate 
has  settled,  decant  the  fluid,  then  add  an  excess  of  ammonia 
water. 

Exp.  117.  To  the  other  half  of  the  HCN  from  Exp.  115  add 
a  little  solution  of  ferrous  sulphate;  also  a  few  drops  of  ferric 
chloride  solution;  then  a  little  KOH  solution;  mix  thoroughly 
and  acidify  with  HCl.  A  blue  precipitate,  Fe4(FeCy6)3,  is  a  test 
for  HCN  or  any  soluble  cyanide. 

Exp.  118.  To  a  few  drops  of  KCN  solution  add  a  little 
yellow  ammonium  sulphide,  (NH4)2S,  and  evaporate  to  dryness. 
Dissolve  in  water;   acidify  with  HCl  and  add  Fe2Cl6  solution. 

Exp.  119.  In  a  small  flask  boil  a  solution  of  KCN.  While 
boiling,  test  the  vapors  for  ammonia  gas.  Solution  of  potassium 
formate  remains  in  the  flask. 

Complete  reaction,  KCN  +  2  H2O  =  ?. 

Exp.  1 20.  To  a  little  dilute  (2%)  solution  of  K4Fe(CN)6  add  a 
little  bromine  water  and  boil.  Prove  the  formation  of  K3Fe(CN)6 
by  use  of  FeCls. 

From  this  experiment  what  is  the  relative  valence  of  iron  in 
the  two  compounds?     Why? 

Exp.  121.  To  a  fresh  solution  of  K3Fe(CN)6  add  a  little  10% 
KOH  solution  and  some  PbO,  shake  and  filter.  To  the  clear 
filtrate  add  FeCls- 

Give  reason  for  the  statement  that  the  PbO  has  acted  as  a 
reducing  agent. 

Exp.  122.  Dissolve  a  piece  of  potassium  ferricyanide,  as 
large  as  a  pea,  in  5  c.c.  water,  add  2  c.c.  of  a  solution  of  potassium 
ferrocyanide.  Dilute  to  a  test-tube  full  with  distilled  water  and 
put  equal  amounts  of  this  solution  into  2  shell  tubes.  Examine 
the  color  through  the  length  of  tube,  then  add  to  one  tube  2  or  3 
drops  of  strong  HCl.  Examine  again  and  notice  that  a  trace  of 
Prussian  blue  h^s  been  produced.     Explain. 


UREA   AND   URIC  ACID 


393 


Experiments  with  Amines  and  Amides.     {Chap.  XXVI.) 

Exp.  123.  Distil  60  c.c.  of  ammonium  acetate  in  a  glass 
retort,  as  in  Fig.  3 5 ,  fitted  with  a  thermometer.  Acetamide  should 
distil  at  about  222°  C.  and  condense  as  a  white  soUd  in  the 
receiver. 


Fig.  35- 

Exp.  124.  In  a  500-c.c.  flask  place  10  grams  of  strong,  fresh, 
bleaching  powder;  add  3  grams  of  acetamide  dissolved  in 
about  10  c.c.  of  water.  Mix  as  thoroughly  as  possible  and  add 
slowly  25  c.c.  of  a  20%  solution  of  NaOH.  Distil  with  steam, 
collecting  distillate  in  15  c.c.  of  cold  water. 

Exp.  125.  To  a  Uttle  of  the  water  solution  of  methyl  amine 
prepared  in  the  last  experiment  add  2  or  3  drops  of^  chloro- 
form and  a  httle  alcohoHc  potash.  This  mixture  upon  warming 
will  give  carbylamine.  Note  the  odor.  Warm  a  little  of  the 
solution  with  a  little  5%  NaOH.  Test  the  vapor  given  off  with 
litmus  paper  and  compare  with  ordinary  quahtative  test  for 

ammonia. 

Urea  and  Uric  Acid. 

Exp.  126.  ^Make  separate  solutions  of  10  grams  of  potassium 

cyanate*  and  8.25  grams  of  ammonium  sulphate.     Mix  and 

*  For  method  of  making  potassiimi  cyanate,  see  Preparation  of  Reagents  and 
Organic  Compounds,  in  the  Appendix. 


394  EXPERIMENTS 

evaporate  on  a  water  bath  in  a  shallow  dish.  Separate  the 
potassium  sulphate  as  the  evaporation  proceeds;  finally,  evapo- 
rate to  dryness  and  extract  with  absolute  alcohol.  Evaporate 
alcohol  and  reserve  the  urea  for  subsequent  experiments.  (See 
Urea,  page  237.) 

Exp.  127.  Heat  a  few  crystals  of  urea  in  a  test-tube  until  they 
fuse  and  no  more  gas  is  given  ofT;  cool,  and  dissolve  the  fused 
mass  in  water;  add  i  or  2  c.c.  of  strong  XaOH  solution, 
then  not  more  than  i  or  2  drops  of  a  1%  CUSO4  solution. 
Xote  the  pink  to  violet  color  produced.  This  constitutes  the 
biuret  reaction  used  in  physiological  chemistry  as  a  test  for 
albumoses  and  peptones.     Biuret  is  formed -from  urea  as  follows: 

/XH. 

20  =  C(         =  )XH-hXH3. 

^XTl2    0  =  C^ 

^XH2 

Exp.  128.  Produce  crystals  of  urea  nitrate  and  oxalate 
(page  238}  and  examine  under  the  microscope.  Repeat  with  urea 
obtained  from  urine. 

This  experiment  ma}'  be  performed  by  concentrating  to 
about  1/5  its  bulk  a  little  urine  and  using  the  concentrated  solu- 
tion as  a  solution  of  urea. 

Exp.  129.  Treat  5  c.c.  of  urea  solution  furine  may  be  used) 
with  a  little  sodium  hypochlorite  or  h}-pobromite ;  note  results 
and  study  reaction  given  on  page  238. 

Exp.  130.  Heat  one-third  of  a  test-tube  of  urine  with  barium 
hydroxide  (baryta-water) ;  test  vapor  with  red  litmus  for  NH3. 

Exp.  131.  Murexide  test  for  uric  acid:  Place  a  very  small 
quantity  of  uric  acid  on  a  porcelain  crucible  cover,  or  in  a  small 
evaporating  dish.  Add  2  or  3  drops  of  strong  nitric  acid 
and  evaporate  to  dr\Tiess  over  a  water-bath.  A  yellomsh-red 
residue  remains,  which  changes  to  a  purplish  red  upon  addition 
of  a  drop  of  strong  XH4OH,   and  purple-\'iolet  upon  further 


EXPERIMEiNTS   WITH   AROMATIC  HYDROCARBONS 


395 


addition  of  a  drop  of  KOH  solution,  the  color  disappearing  upon 
standing  or  upon  the  application  of  heat.  (Difference  from 
xanthin,  which  also  gives  a  deeper  red  color.) 

Exp.  132.     Repeat  No.  131,  using  caffein  in  place  of  uric  acid. 

Exp.  133.  Heat  a  httle  sodium  acid  urate  in  a  dilute  solution 
of  NaH2P04.  Allow  to  cool,  and  examine  any  deposit  for  uric 
acid  crystals.  Test  reaction  of  solution  both  hot  and  cold 
(page  242). 

Exp.  134.  Mix,  and  allow  to  stand  for  some  time  at  reduced 
temperature,  30  c.c.  of  urine  (a  2%  urea  solution),  2  or  3  c.c.  of 
strong  NaoCOs  solution,  and  5  c.c.  of  saturated  NH4CI  solution. 

A  precipitate  consists  of  ammonium  urate. 

Examine  under  the  microscope  and  make  murexide  test. 


Experiments  with  Aromatic  Hydrocarbons. 

Exp.  135.  Into  a  small  and  thoroughly  dry  flask  (250  c.c.) 
introduce  about  50  grams  of  a  mixture  consisting  of  i  part  of 
benzoic  acid  and  2, parts  of  quick- 
lime; connect  with  a  beaker  con- 
denser (Fig.  36)  and  heat.  Ben- 
zene (benzol)  distils  over: 

CaO  -f  C6H5COOH  = 

CaCOs  +  CeHe. 

Exp.  136.  Turn  a  Httle  of 
the  benzene  prepared  in  the  last 
experiment  onto  some  water 
contained  in  a  porcelain  capsule. 
Set  fire  to  it  and  note  that  it 
burns  with  a  smoky  flame.  Cool  a  few  cubic  centimeters  of  pure 
benzene  contained  in  a  narrow  test-tube  by  immersion  in  a 
freezing  mixture  of  ice  and  salt. 

Exp.  137.     In  a  wide  test-tube  mix  5  c.c.  of  concentrated 
H2SO4  with  about  half  its  volume  of  strong  HNO3;    cool  in  ice- 


FiG.  36. 


396  EXPERIMENTS 

water  or  cold  running  water,  and  add  very  slowly  about  2  c.c. 
of  benzene.  Nitrobenzene  is  formed  and  may  be  separated  as 
a  heavy  oily  liquid  by  pouring  the  mixture  into  an  excess  of 
water.     Notice  the  odor  of  oil  of  bitter  almonds. 

Exp.  138.  Observing  the  same  precaution  against  overheat- 
ing as  given  in  Exp.  137  reduce  nitrobenzene  to  amino-benzene 
as  follows:  In  a  large  test-tube  or  small  flask  place  i  or  2  c.c. 
of  nitrobenzene  with  three  times  its  weight  of  tin  powder.  To 
this  add  10  or  15  c.c.  of  strong  HCl  in  successive  small  portions, 
keeping  cool  as  indicated.  The  odor  of  nitrobenzene  should  be 
replaced  by  that  of  aniline. 

Exp.  139.  Heat  a  mixture  of  2  c.c.  of  aniline,  5  c.c.  of  water 
and  I  c.c.  of  strong  sulphuric  acid  to  the  boiling  point;  then  set 
aside  where  it  may  cool  slowly.  Crystals  of  aniline  sulphate 
wiU  separate. 

Exp.  140.  Repeat  preceding  experiment,  using  5  c.c.  of 
aniline,  5  c.c.  of  water  and  10  c.c.  of  strong  hydrochloric  acid. 
When  the  mixture  has  become  thoroughly  cold  filter  off  the 
crystals  of  aniline  hydrochloride  and  dry  in  a  current  of  air.  Test 
solubihty  in  water,  using  only  a  very  little  of  the  crystallized  salt. 

Exp.  141.  Place  5  c.c.  of  an  aqueous  solution  of  aniline  in 
each  of  three  test-tubes.  Add  to  the  first  a  few  drops  of  bromine 
water;  to  the  second  a  few  drops  of  dilute  ferric  chloride;  and 
to  the  third  a  solution  of  h}^ochlorite  of  calcium  or  sodium. 

Exp.  142.  Shake  together  in  a  test-tube  i  part  of  aniline  oil 
and  5  parts  of  water.     Is  the  oil  soluble  in  water? 

Agitate  with  HCl  added  in  small  portions  till  liquid  becomes 
clear.     Explain. 

Exp.  143.  To  a  few  cubic  centimeters  of  a  3%  phenol  solu- 
tion add  dilute  bromine  water.  A  yellowish- white  crystalline 
precipitate  of  tribromphenol  is  produced  (see  page  184). 

Exp.  144.  To  an  aqueous  solution  of  phenol  add  a  few  drops 
of  solution  of  ferric  chloride. 

Exp.  145.     To  5  c.c.  of  an  aqueous  solution  of  phenol  add 


EXPERIMENTS  WITH  AROMATIC  HYDROCARBONS     '    397 

one  quarter  its  volume  of  ammonia  water  and  then  a  few  drops 
of  sodium  hypochlorite  solution.  Mix  and  warm.  A  blue-green 
color  develops  which  turns  red  upon  addition  of  hydrochloric 
acid  to  slight  acid  reaction. 

Exp.  146.  Repeat  Exps.  143  and  144,  using  an  aqueous  solu- 
tion of  cresol  in  place  of  phenol. 

Exp.  147.  To  a  test-tube  1/3  full  of  nitric  acid  (50%  abso- 
lute HNO3),  add,  I  drop  at  a  time,  about  i  c.c.  of  phenol  with 
constant  agitation.  When  the  phenol  has  all  been  added  heat 
carefully  to  boiling.  Allow  to  cool  slowly  when  trinitrophenol 
will  be  precipitated. 

Exp.  148.  Evaporate  a  few  drops  of  a  1%  solution  of  potas- 
sium nitrate  to  dryness  in  a  small  porcelain  capsule.  Add  2  c.c. 
of  phenoldisulphonic  acid;*  stir  thoroughly,  and  keep  hot  for 
three  to  five  minutes;  dilute  with  water,  make  strongly  alkaline 
with  ammonia,  and  note  the  intense  yellow  color  of  ammonium 
picrate.  The  reaction  is  used  as  a  test  for  nitrates  in  drinking 
water. 

Exp.  149.     Determine  melting-point  of  benzoic  acid. 

Exp.  150.  Arrange  two  watch  glasses  of  equal  size  with  the 
concave  surfaces  together  and  a  piece  of  filter  paper  stretched 
between  them.  The  glasses  may  be  held  together  with  a  small 
brass  clamp. 

A  little  benzoic  acid  placed  in  the  lower  glass  may  be  sub- 
limed by  means  of  a  gentle  heat  through  the  paper  and  collected 
upon  the  upper  glass.  Examine  the  sublimate  by  polarized 
light.     See  Plate  V,  Fig.  5,  opposite  page  204, 

Exp.  151.  With  an  aqueous  solution  of  benzaldehyde  deter- 
mine whether  ToUen's  test  for  aldehydes  (Exp.  85)  is  applicable 
to  aromatic  compounds. 

Exp.  152.  ^  Boil  10  c.c.  of  oil  of  wintergreen  with  a  little  of 
20%  NaOH;  keep  the  volume  constant  by  frequent  addition  of 
water.  When  the  oil  has  entirely  disappeared,  cool  and  add  HCl 
*  For  method  of  preparation  of  phenoldisulphonic  add,  see  Appendix. 


398  EXPERIMENTS 

to  acid  reaction.  Salicylic  acid  will  separate,  white  and  crystal- 
line. 

Exp.  153.  To  a  dilute  solution  of  sodium  salicylate,  or  satu- 
rated aqueous  solution  of  salicylic  acid,  add  a  few  drops  of 
Fe2Cl6.  A  slight  amount  of  salicylates  in  the  urine  will  produce 
this  color  when  a  test  is  being  made  for  diacetic  acid  (q.  v.). 

Exp.  154.  Mix  in  a  large  test-tube  or  small  flask  a  httle  dry 
slaked  lime  and  sahcylic  acid,  connect  with  a  beaker  condenser 
(see  cut  on  page  395)  and  distil.  Test  distillate  for  phenol. 
Write  reaction. 

Note.  —  After  the  first  heating,  the  tube  containing  the  lime  and  acid  may  be 
inclined  so  that  any  moisture  in  distillate  will  run  into  collecting  tube  rather  than 
back  onto  the  mixture. 

EXPERIMENTS  FOR  PHYSIOLOGICAL  CHEMISTRY. 

Preparation  of  Oxidase. 

Exp.  155.  Clean  thoroughly  a  small  potato  and  grate  the 
skin  into  a  small  beaker;  cover  with  water  and  allow  to  stand 
in  a  cool  place  for  an  hour.  Filter  through  coarse  paper.  Turn 
about  5  c.c.  of  the  filtrate  slowly  into  25  c.c.  of  strong  alcohol. 
The  enzyme  will  be  precipitated.     Filter  and  test  as  follows: 

Exp.  156.  Transfer  the  moist  precipitate  from  the  above 
experiment  into  half  a  test-tube  of  distilled  water.  Shake  fre- 
quently for  about  ten  minutes  and  filter.  The  filtrate  will 
contain  oxidizing  enzymes  in  solution.  Divide  the  solution  into 
two  parts;  to  one  add  a  few  drops  of  tincture  of  guaiacum,  and 
to  the  other  a  little  of  a  1%  solution  of  pyrocatechol.  The 
guaiacum  gives  a  blue  color,  and  the  pyrocatechol  a  red-brown 
color  in  the  presence  of  oxidizing  enzymes. 

Experiments  with  Enzymes. 

Hydrolytic  enzymes  produce  cleavage  of  the  molecule. 
Exp.   157.     Take  five   test-tubes,  a-h-c-d-e.     Make  a  thin 
paste  by  rubbing  one-sixth  of  a  yeast  cake  with  water,  and  place 


EXPERIMENTS  WITH  ENZYMES 


399 


a  little  in  each  of  the  five  tubes;  then  fill  a  with  a  dilute  glucose 
solution;  b  with  a  dilute  solution  of  milk  sugar;  c  with  dilute 
solution  of  cane  sugar;  to  d  add 
a  little  invertase  (an  enzyme  from 
the  mucosa  of  the  small  intes- 
tine of  a  pig)  .  (see  Appendix) ; 
then  fill  with  the  same  solution 
used  for  c.  Prepare  e  exactly 
the  same  as  d  except  that  be- 
fore adding  the  sugar  solution 
the  enzymes  are  boiled  for  at  least 
one  minute.  Fit  each  tube  with 
short  delivery  tube  and  allow  to 
stand  overnight. 

Exp.  158.  Take  four  test-tubes, 
a-b-c-d,  arrange  as  indicated  in 
Fig.  37,  and  half  fill  each  with  some 
thin  starch  paste  (see  page  430  of 
Appendix).  Into  a  put  a  little  of 
the  yeast  from  last  experiment; 
into  b  a  little  pepsin  solution;  into 
c  a  little  saliva  (the  enzyme  of  the  saHva  in  ptyalin);  into  d  a 
little  invertase  as  used  in  preceding  experiment.  Warm  all  the 
tubes  to  about  37  or  38°  C,  and  allow  to  stand  overnight;  then 
test  contents  of  each  tube  for  a  reducing  sugar  which  may  have 
been  produced  from  the  starch.     (Use  Exp.  167.) 

Exp.  159.  The  student  may  prepare  a  fat-splitting  enzyme 
(lipase)  from  an  animal  source,  pig's  pancreas,  according  to 
direction  in  the  appendix;  or  from  a  vegetable  source,  castor 
beans,  as  follows : 

Fat  Digestion  with  Lipase  {Castor  Bean).  —  Grind  with  the 
powder,*  in  the  order  named,  5  c.c.  N/io  sulphuric  acid,  5  c.c.  of 
neutral  cotton  oil  (sp.  gr.  0.92)  and  5  c.c.  lukewarm  water.     The 

*  For  preparation  of  powder,  see  page  428. 


Fig.  37. 


400  EXPERIMENTS 

water  should  be  added  a  little  at  a  time  and  thoroughly  worked 
into  the  mixture  so  that  at  the  end  of  the  operation  a  good 
emulsion  is  secured.  Cover  the  evaporating  dish  and  let  stand 
in  a  warm  place  overnight. 

Add  50  c.c.  of  alcohol,  10  c.c.  ether,  and  a  few  drops  phenol- 
phthalein  and  titrate  with  N/i  sodium  hydrate.  Calculate  the 
amount  of  fatty  acid  and  the  per  cent  of  fat  digestion. 

Exp.  160.  To  one-third  of  a  test-tube  of  mUk,  colored  slightly 
blue  with  nearly  neutral  Utmus  solution,  add  half  as  much 
solution  of  lipase  (fresh  pancreatic  extract)  and  keep  at  about 
40°  C.  for  twenty  to  thirty  minutes.  Sufficient  fat  acid  should 
be  separated  to  change  the  blue  Utmus  to  red.     Write  reaction. 

Exp.  161.  Dialyse  thoroughly  some  saliva,  using  three  or 
four  changes  of  water,  then  see  if  the  effect  of  dialysis  on  the 
amylolytic  ferment  of  the  saliva  is  the  same  as  on  the  amylolytic 
ferment  of  the  pancreatic  juice,  page  322. 

Experiments  with  Sugars. 

Exp.  162.  Fill  a  test-tube  about  one  third  full  of  dry  straw. 
Cover  with  10%  hydrochloric  acid;  boil,  collecting  the  distillate 
in  a  dry  tube.  Divide  the  distillate  into  two  parts,  and  make 
the  following  tests  for  furfuraldehyde  which  has  been  produced 
from  the  pentose  contained  in  the  straw.  Treat  the  contents 
of  one  tube  with  a  little  aniline  and  hydrochloric  acid.  Red 
coloration  indicates  the  presence  of  furfuraldehyde.  To  the 
contents  of  the  other  tube  add  a  Httle  solution  of  casein  (skimmed 
milk)  and  underlay  with  strong  sulphuric  acid.  Furfurol  will 
give  a  blue  or  purple  line  at  the  point  of  contact  of  the  two  liquids. 

Monosaccharides.  —  Exp.  163.  Test  for  C  and  H,  using 
cane-sugar.  Make  closed-tube  test  for  H,  which  is  given  off  as 
H2O,  and  for  C,  which  remains  as  such  in  tube.  (See  page  105.) 
Write  reactions. 

Exp.  164.  Molisch's  Test  for  Carbohydrates. — To  a  few 
cubic  centimeters  of  a  3%  glucose  solution  add  a  few  drops  of 


EXPERIMENTS   WITH  SUGARS 


401 


an  alcoholic  solution  of  a-naphthol,  and  carefully  underlay  the 
mLxture  with  strong  H0SO4. 

Exp.  165.  To  a  few  cubic  centimeters  of  CUSO4  solution 
in  a  test-tube  add  a  little  NaOH.     Boil  and  write  reaction. 

Exp.  166.  Repeat  Exp.  165  with  the  addition  of  Rochelle 
salt;  if  solution  remains  clear  on  boiling,  add  a  few  drops  of  a 
glucose  solution. 

Exp.  167.  Fehling's  Test  for  Sugars.  — Take  about  5  c.c.  of 
Fehling's  solution*  made  by  mixing  equal  parts  of  the  CUSO4 
solution  and  the  alkahne  tartrate  on  side  shelf.  Boil  and  add 
immediately  a  few^  drops  of  glucose  solution. 
Set  aside  for  a  few  minutes,  watching  the  results. 

Exp.  168.  Repeat  Exp.  167,  using  diabetic 
urine  instead  of  glucose. 

Exp,  169.  Repeat  Exp.  167  without  heat 
and  allow  to  stand  for  twenty-four  hours. 

Exp.  170.  5  c.c.  of  Benedict's  solution  (for 
prep,  see  Appendix).  Add  8  or  10  drops  of 
a  2%  glucose  solution.  Heat  the  mixture  to 
boiling;  keep  at  this  temperature  for  one  or  two 
minutes. 

Exp.  171.  Barfoed's  Test.  — To  about  5  c.c. 
of  Barfoed's  reagent  add  a  few  drops  of  glucose 
solution;  boil  and  set  aside  for  a  few  minutes, 
watching  results. 

Exp.    172.     Fermentation    Test.  —  Fill    the 
"fermentation  tube"  (Fig.  38)  found  in  the  desk 
with  glucose  solution;   add  a  little  yeast;  insert  stopper,  with 
long  arm  of  tube  extending  into  glucose  mixture  nearly  to  bot-' 
tom  of  tube,  and  aUow  it  to  stand  upright,  in  a  warm  place, 
overnight.     On  the  next  day,  test  the  gas,  with  which  the  tube 
is  filled,  with  lime  water. 

Exp.    173.     Phenylhydrazine   Test. 

*  For  preparation,  see  Appendix. 


Place   about    5    c.c.   of 


402  EXPERIMENTS 

glucose  solution  in  a  test-tube;  add  an  equal  volume  of  phenyl- 
hydrazine  solution;  keep  the  tube  in  boiling  water  for  thirty 
minutes.  Allow  to  cool  gradually.  Examine  the  precipitate 
microscopically  and  sketch  the  crystals. 

Disaccharides.  —  Exp.  174.  Use  dilute  solutions  of  cane- 
sugar,  milk-sugar,  and  maltose,  and  make  on  each  Fehhng's 
test  (Exp.  167),  Barfoed's  test  (Exp.  171),  and  the  phenylhy- 
drazine  test  (Exp.  173).  Sketch  the  different  osazone  crystals 
obtained. 

Exp.  175.  To  a  dilute  solution  of  cane-sugar  add  a  few 
drops  of  dilute  H2SO4  and  boil  for  five  minutes.  Cool  the 
mixture  and  make  sHghtly  alkaline  with  NaOH.  With  this  solu- 
tion perform  Exps.  167,  171,  and  173.  Explain  results.  Com- 
pare with  Exp.  174. 

Experiments  with  Starches  and  Cellulose. 

Polysaccharides.  —  Exp.  176.  Examine  potato,  corn,  and 
wheat  starch  under  the  microscope,  use  a  drop  of  water  and 
a  cover  glass.  Sketch  the  granules  of  each  in  notebook,  and, 
while  still  on  the  slide,  treat  w^ith  a  dilute  iodine  solution.  Note 
changes  in  appearance  of  granules. 

Exp.  177.  Preparation  of  starch.  Grate  a  Httle  raw  potato. 
Mix  thoroughly  with  water  and  strain  through  ",bolting"  cloth 
or  stout  coarse  musUn.  After  the  Hquid  has  run  through,  com- 
press the  cloth  by  twisting  till  no  more  liquid  can  be  squeezed 
out.  The  starch  has  passed  through  the  cloth  and  may  be 
washed  by  decantation,  dried  on  filter  paper,  examined,  and  used 
for  the  following  experiments: 

Exp.  178.  Make  some  starch  paste  by  rubbing  one  gram  of 
starch  to  a  smooth,  thin  paste  with  water;  then  slowly  pour  it 
into  100  c.c.  of  boiling  water,  stirring  constantly.  With  this 
solution  compare  a  one  per  cent,  solution  of  dextrine  and  a  solu- 
tion of  glycogen  *  as  follows : 

*  For  the  isolation  of  glycogen,  see  Appendix. 


EXPERIMENTS  WITH  FATS  AND  OILS  403 

(a)  Treat  each  by  boiling  with  Fehling's  solution. 

(b)  Add  to  5  c.c.  of  each  a  few  drops  of  tannic-acid  solu- 
tion. 

(c)  To  each  solution  add  a  drop  of  iodine  solution.  Note 
color  of  mixture  while  cold.  Heat  nearly  to  boiling  and  allow 
to  cool  again,  watching  the  color  during  process. 

(d)  To  5  c.c.  of  each  solution  add  twice  its  volume  of  66% 
alcohol. 

(e)  Tabulate  results  of  the  tests  and  formulate  method  of 
distinguishing  these  three  substances  from  one  another. 

Experiments  with  Fats  and  Oils. 

Exp.  179.  Test  solubility  of  olive  oil  in  water,  ether,  chloro- 
form, and  alcohol,  carefully  avoiding  the  vicinity  of  a  flame. 

Exp.  180.  Let  one  or  two  drops  of  an  ether  solution  of  the 
oil  drop  on  a  plain  white  paper,  also  an  ether  solution  of  a  volatile 
oil  found  on  side  shelf.  Watch  behavior  of  the  two  oils,  and 
report  differences,  if  any. 

Exp.  181.  Dissolve  a  little  butter  in  warm  alcohol,  examine 
with  the  microscope,  and  micropolariscope  the  crystals,  which 
separate  on  cooling. 

Note.  —  If  possible  perform  the  next  experiment  in  triplicate,  i.e.,  carry  three 
experiments  along  at  the  same  time  using  for  "fat"  the  glyceryl  ester  of  the  three 
most  comm.on  fat  acids:  Olein  (lard  oil  or  olive  oil),  Stearin  (beef  fat  or  tallow), 
Palmatin  (bayberry  wax  or  tallow,  which  contains  a  large  amount  of  free  palmitic 
acid). 

Exp.  182.  Saponification.  —  To  about  two  grams  of  solid  fat 
placed  in  a  narrow  beaker,  or  150-c.c.  Erlenmeyer  flask,  add  10 
or  15  c.c.  of  alcoholic  solution  of  potassium  hydroxide.  Allow 
the  beaker  to  stand  on  the  water  bath  till  the  alcohol  is  entirely 
evaporated,  then  dissolve  the"  resulting  soap  in  water;  filter,  if 
necessary,  to  obtain  a  clear  solution  and  make  the  following  tests : 

(a)  Add  to  a  portion  of  solution  a  saturated  solution  of 
sodium  chloride.     What  takes  place? 


404  EXPERIMENTS 

(b)  To  another  portion  add  a  few  cubic  centimeters  of  a  so- 
lution of  calcium  or  magnesium  chloride.     Explain  the  results. 

(c)  Pour  the  remainder  slowly,  and  with  constant  stirring, 
into  warm  dilute  HoSOj,  and  heat  on  the  water  bath.  What  is 
the  result?  Write  the  equation.  Transfer  the  mixture  to  a 
filter-paper  which  has  been  moistened  with  hot  water,  and 
wash  with  hot  water  till  all  H2SO4  is  removed.  Reserve  the 
filtrates. 

Exp.  183.     Fatty  acids. 

(a)  Dissolve  a  portion  of  the  above  precipitates  (182  c)  by 
warming  with  strong  alcohol.  Test  the  reaction  of  the  solution. 
Examine  the  crystals,  which  separate  upon  standing,  with  micro- 
scope and  micropolariscope.     (Plate  VII,  Fig.  3,  page  287.) 

(b)  Add  to  a  portion  a  few  cubic  centimeters  of  a  strong 
NaoCOs  solution,  and  heat  till  the  fatty  acids  dissolve.  Cool. 
What  takes  place?     Explain  the  reaction.     Reserve  the  jelly. 

Exp.  184.  Neutralize  the  filtrates  of  Exp.  182  c  and  evaporate 
almost  to  dryness  on  the  water  bath.  Extract  with  alcohol 
and  evaporate.  Note  the  taste.  Heat  another  portion  of  the 
residue  with  a  little  powdered  dry  KHSO4  in  a  dry  test-tube, 
and  note  the  odor,  which  is  due  to  acrolein,  CHo  =  CH  —  CHO. 
Fuse  some  borax  and  glycerin  on  a  platinum  loop:   green  color. 

Exp.  185.  Emulsification.  —  (a)  Put  i  to  2  c.c.  of  a  solution 
of  sodium  carbonate  (0.25%)  on  a  watch  glass,  and  place  in 
the  center  a  drop  of  rancid  oil.  The  oil-drop  soon  shows  a 
white  rim,  and  a  white  milky  opacity  extends  over  the  solution. 
Note  with  the  microscope  the  active  movements  in  the  vicinity 
of  the  fat-drop,  due  to  the  separation  of  minute  particles  of  oil 
(Gad's  experiment). 

(6)   Take  six  test-tubes  and  arrange  as  follows: 

1.  10  c.c.  of  a  0.2%  Na2C03  solution  +  2  drops  of  neutral 

oil. 

2.  10  c.c.  of  a  0.2%  Na^COs  solution  +  2  drops  of  rancid 

oil. 


GENERAL  PROTEIN  REACTIONS  '       405 

3.  10  c.c.  of  soap- jelly  (see  151  b),  warm,  +  2  drops  of 

neutral  oil. 

4.  10  c.c.  of  albumin  solution  +  2  drops  of  neutral  oil. 

5.  10  c.c.  of  gum-arabic  solution  -f  2  drops  of  neutral  oil. 

6.  10  c.c.  of  water  -f-  2  drops  of  neutral  oil. 

Shake  all  the  mixtures  thoroughly  and  note  the  results. 
What  conclusions  do  you  form  relative  to  the  influence  of  con- 
ditions upon  emulsification? 

(c)    Examine  a  drop  of  an  emulsion  under  the  microscope. 

General  Protein  Reactions. 

Exp.  186.  Test  dried  egg-albumin  for  C,  H,  S,  and  N,  ac- 
cording to  the  methods  described  on  pages  194  and  195.  Test 
casein  for  phosphorus,  and  dried  blood  for  iron. 

There  are  several  reactions  which  are  common  to  nearly  all 
proteins.  For  the  following  tests  use  a  solution  of  egg-albumin 
(1/50)  in  water,  as  a  general  type  of  a  protein. 

I.   Color  Reactions. 

Exp.  187.  Xanthoproteic  Test.  —  To  10  c.c.  of  the  albumin 
solution  add  one  third  as  much  concentrated  HNO3;  there  may 
or  may  not  be  a  white  precipitate  produced  (according  to  the 
nature  of  the  protein  and  the  concentration).  Boil;  the  pre- 
cipitate or  liquid  turns  yellow.  When  the  solution  becomes 
cool  add  an  excess  of  NH4OH,  which  gives  an  orange  color. 
(This  color  constitutes  the  essential  part  of  the  test.) 

Exp.  188.  Milton's  Test.  ^  Add  a  few  drops  of  Millon's  re- 
agent* to  a  part  of  the  albumin  solution.  A  precipitate,  which 
becomes  brick-red  upon  heating,  forms.  The  liquid  is  colored 
red  in  the  presence  of  non-coagulable  protein  or  minute  traces 
of  albmnin. 

*  Mercuric  nitrate  in  nitric  acid.  For  the  preparation  of  this  and  other  re- 
agents, see  Appendix. 


406  EXPERIMENTS 

Exp.  189.  Piotrowskis  Test.  —  To  a  third  portion  add  2 
drops  of  a  very  dilute  solution  of  CUSO4,  and  then  5  to  10  c.c. 
of  a  40%  solution  of  NaOH.  The  solution  becomes  blue  or 
violet.  Proteoses  and  peptones  give  a  rose-red  color  (biuret 
reaction)  if  only  a  trace  of  copper  sulphate  is  used;  an  excess 
of  CUSO4  gives  a  reddish- violet  color,  somewhat  similar  to  that 
obtained  in  the  presence  of  other  proteins.  This  test  responds 
with  all  proteins. 

Exp.  190.  Hopkins-Cole  reaction:  MLx  2  or  3  c.c  of  the 
unknown  protein  solution  with  3  or  4  c.c.  of  the  reagent  (gly- 
oxylic  acid).  Then  carefully  superimpose  upon  5  c.c.  of  strong 
sulphuric  acid  in  another  test-tube. 

The  glyoxyhc  acid  is  made  by  the  reduction  of  oxalic  acid 
with  nascent  hydrogen  produced  by  the  action  of  sodium  amal- 
gam and  water.     Formula  is  CHO.COOH. 

2.   General  Precipitants. 

Proteins  are  precipitated  from  solution  by  the  following  re- 
agents (peptones  are  exceptions  in  some  cases) : 

Exp.  191.  Acetic  Acid  and  Potassic  Ferrocyanide. — Make 
part  of  the  solution  to  be  tested  strongly  acid  with  acetic  acid, 
and  add  a  few  drops  of  potassic  ferrocyanide  solution.  A  white 
fiocculent  precipitate  is  formed  (not  with  peptones). 

Exp.  192.  Alcohol.  —  To  another  part  add  one  or  two  vol- 
umes of  alcohol. 

Exp.  193.  Tannic  Acid. — Make  the  solution  acid  with 
acetic  acid,  and  add  a  few  drops  of  tannic-acid  solution. 

Exp.  194.  Potassio-mer curie  Iodide.  —  ]\Iake  acid  another 
portion  with  HCl,  and  add  a  few  drops  of  the  reagent. 

Exp.  195.  Neutral  Salts.  —  Certain  neutral  salts  precipitate 
most  proteins.  (NH4)2S04  added  to  complete  saturation  to 
protein  solutions,  faintly  acid  with  acetic  acid,  precipitates  all 
proteins,  with  the  exception  of  peptones. 


EXPERIMENTS   WITH   ALBUMIN  AND  GLOBULIN  407 

Experiments  with  Albumin  and  Globulin. 

The  albumins  and  globulins  respond  to  all  the  general  protein 
reactions.     Experiments  187  to  195. 

Exp.  196.  A  specimen  of  solid  egg-albumin,  prepared  by 
evaporating  a  solution  to  dryness  at  40°  C,  is  provided.  Test 
its  solubility  in  water,  alcohol,  acetic  acid,  KOH  solution,  and 
concentrated  HCl.     Report  results. 

Perform  the  following  additional  experiments,  using  a  dilute 
(1/50)  solution  of  egg-albumin. 

Exp.  197.  Nitric-acid  Test.  —  Take  15  c.c.  of  the  solution  in 
a  wine-glass,  incline  the  glass,  and  allow  5  c.c.  of  concentrated 
HNO3  to  run  slowly  down  the  side  to  form  an  under  layer. 
What  other  proteins  respond  to  this  test? 

Exp.  198.  Picric-acid  Test.  —  Take  a  portion  of  the  albumin 
solution  and  add  a  few  drops  of  a  solution  of  picric  acid  acidified 
with  citric  acid  (Esbach's  reagent).  What  other  proteins  re- 
spond to  tills  test? 

Exp.  199.  Action  of  {NH^iSOa.  —To  10  c.c.  of  the  albumin 
solution  in  a  test-tube  add  some  solid  (NH4)2S04,  shaking  until 
solution  is  thoroughly  saturated.  Allow  to  stand  a  little  while, 
shaking  occasionally,  then  filter,  saving  the  filtrate  to  test  for 
albumin  by  the  heat  test.  Report  result.  Test  the  solubility 
of  the  precipitate  on  the  filter-paper. 

Exp.  200.  Action  of  MgSOi. — Perform  an  experiment 
similar  to  Exp.  199  using  solid  MgS04  instead  of  (NH4)2S04. 
With  what  results? 

Exp.  201.  Salts  of  the  Heavy  Metals.  —  Note  the  action  of 
the  following:  AgNOg,  HgCls,  CUSO4,  Pb(C2H302)2.  Use  solu- 
tions of  the  salts  and  of  albumin. 

Why  is  white  of  egg  an  antidote  in  cases  of  metallic  poisoning? 

The  following  tests  serve  to  distinguish  the  globuhns  from 
other  proteins. 

The  tests  may  be  made  upon  blood  serum,  or  upon  a  globulin 


4o8  EXPERIMENTS 

(edestin)  which  may  be  separated  from  hemp  seed  according  to 
preparation  in  Appendix,  page  434. 

Globulins. 

Exp.  202.  Action  of  CO2.  —  To  5  c.c.  of  blood  serum  add 
45  c.c.  of  ice-cold  water.  Place  the  mixture  in  a  large  test-tube 
or  cylinder,  surround  it  with  ice-water,  and  pass  through  it  a 
stream  of  CO2.  A  fiocculent  precipitate  (paraglobuhn)*  will  be 
formed. 

Exp.  203.  Precipitation  by  Dialysis.  —  Into  a  parchment 
dialyzing  tube,  previously  soaked  in  distilled  water,  pour  20  c.c. 
of  serum,  swing  the  tube,  with  its  contents,  into  a  large  vessel 
of  distilled  water,  which  is  to  be  changed  at  intervals.  Let 
stand  twenty-four  hours,  then  examine  the  serum  in  the  dialyz- 
ing tube;  it  will  contain  a  fiocculent  precipitate  of  paraglobuhn. 
Give  explanation  of  cause  of  precipitation. 

Exp.  204.  Pour  a  solution  of  globulin,  drop  by  drop,  into  a 
large  volume  of  distilled  water  (in  a  beaker).  What  takes 
place?     Explain. 

Exp.  205.  Precipitation  by  Magnesium  Sulphate.  — •  Saturate 
about  5  c.c.  of  globuhn  solution  with  solid  magnesium  sulphate. 
A  heavy  precipitate  will  be  formed.  Compare  this  with  the 
action  of  the  same  salt  on  the  egg-albumin  solution.  Paraglob- 
uhn is  so  completely  precipitated  by  this  salt  that  the  method 
is  used  for  its  quantitative  estimation. 

Experiments  with  Keratin  and  Gelatin. 

Keratins  are  characterized  by  their  insolubility,  and  by  their 
high  content  of  loosely  combined  sulphur. 

Exp.  206.  Test  solubility  of  keratin  (nail  or  horn)  in  water, 
acids,  alkalies,  gastric  and  pancreatic  juices. 

Exp.  207.     Warm  a  bit  of  keratin  with  5  c.c.  strong  NaOH 

*  Paraglobulin  is  a  name  applied  to  the  globulin  separated  from  blood  serum. 


EXPERIMENTS  WITH  MILK  '     409 

solution  for  a  few  minutes,  and  add  a  few  drops  of  a  lead  acetate 
solution.     What  is  the  result? 

Exp.  208.  With  a  solution  of  gelatin  make  the  usual  tests 
for  protein. 

Exp.  209.  Precipitate  gelatin  from  dilute  solution  with  the 
following  reagents: 

[a)   Tannic  acid. 

(6)   Alcohol. 

(c)   Acetic  acid  and  potassium  ferrocyanide. 

id)    Mercuric  chloride. 

(e)    Picric  acid. 

Experiments  with  Milk. 

Exp.  210.  Examine  microscopically  whole  milk,  skim-milk, 
and  cream.  Note  the  relative  amounts  of  fat  in  the  three 
varieties. 

Exp.  211.  Shake  a  little  cream  with  chloroform  in  a  test- 
tube;  separate  the  chloroform,  evaporate,  and  melt  the  fat 
residue  obtained;  allow  it  to  cool  slowly,  when  fat  crystals  will 
be  obtained,  which  may  be  examined  under  the  microscope  and 
micropolariscope . 

Exp.  212.  With  a  lactometer  take  the  specific  gravity  of 
whole  mUk  and  skim-milk  and  explain  the  difference  in  results. 

Exp.  213.     Test  the  reaction  of  milk  with  Htmus. 

Exp.  214.  Dilute  some  milk  with  six  or  seven  times  its 
volume  of  water,  and  add  acetic  acid  drop  by  drop  till  the 
casein  is  precipitated.  Filter  and  reserve  the  precipitate.  Test 
the  filtrate  for  proteins,  if  any  remain;  determine  if  possible 
their  character. 

Exp.  215.     Test  another  portion  of  the  filtrate  for  carbohy- 
drates, determining  the  variety  present. 

Exp.  216.  To  50  c.c.  of  milk  add  a  few  drops  of  rennin 
solution;  keep  at  a  temperature  of  40°  C.  for  a  few  minutes, 
and  explain  results.' 


4IO  EXPERIMENTS 

Exp.  217.  Take  a  portion  of  the  precipitated  casein  from 
Exp.  214,  digest  at  40°  C.  with  pepsin  HCl  for  twenty  minutes 
or  half  an  hour.  While  digesting,  test  other  portions  of  casein, 
for  solubility  in  water,  in  dilute  acid  and  dilute  alkali.  Test 
also  a  portion  for  phosphorus  by  boiUng  in  a  test-tube  with 
dilute  nitric  acid,  cooling  to  at  least  50°  C,  and  adding  ammo- 
nium molybdate  solution. 

Exp.  218.  To  a  little  skim-milk  contained  in  a  test-tube  add 
a  saturated  solution  of  ammonium  sulphate. 

Experiments  with  Mucin. 

Exp.  219.  To  a  solution  of  mucin*  found  on  the  side  shelf 
add  acetic  acid  till  precipitation  takes  place.  Settle  filter, 
wash,  and  test  solubility  in  water,  dilute  alkali  solution  and 
5%  HCL 

Exp.  220.     Make  color- tests  for  proteins. 

Exp.  221.  Boil  a  little  mucin  solution  with  dilute  HCl  for 
several  minutes.     Cool,  neutralize,  and  test  for  sugar. 

Experiments  with  Protein  Derivatives. 

Exp.  222.  Preparation  of  Metaprotein.  —  To  a  solution  of 
egg-albumin  add  a  few  drops  of  a  0.5%  solution  of  NaOH,  and 
warm  gently  for  a  few  minutes.  With  the  solution  thus  ob- 
tained make  the  following  tests: 

Exp.  223.  (a)  EJfect  of  Heating.  —  Boil  some  of  the  solution 
and  report  result. 

(b)  EJfect  of  Neutralizing.  — •  Add  a  drop  of  Htmus  solution, 
and  cautiously  neutralize. 

Acid  Metaprotein. 

Exp.  224.     Add  a  small  quantity  of  a  0.2%  HCl  solution  to  a 
solution  of  egg-albumin,  and  warm  at  40°  C.  for  one  half  to  one 
hour.     Or  cover  with  an  excess  of  0.2%  HCl  some  meat  cut 
*  For  preparation  of  mucin  solution  from  navel  cord,  see  Appendix. 


EXPERIMENTS   WITH   PEPTONES  411 

into  fine  pieces,  and  expose  for  a  while  to  a  temperature  of 
40°  C.  Filter.  With  either  of  the  solutions  thus  obtained 
make  same  tests  as  on  alkali  metaprotein,  and  compare  results. 
How  distinguish  between  them? 

Experiments  with  the  Proteoses. 

Alhumoses  {Hemialbumose) .  —  This  name  includes  four  closely 
allied  forms  of  albumose,  namely:  (i)  Protoalbumose,  (2) 
Deuteroalbumose;  (3)  Heteroalbumose ;  (4)  Dysalbumose,  an 
insoluble  modification  of  heteroalbumose.  Commercial  peptone, 
which  is  substantially  a  mixture  of  albumoses  and  peptones,  will 
be  given  out  for  use. 

Exp.  225.  Make  a  solution  of  the  peptone  in  water,  filter 
if  necessary,  and  saturate  with  soHd  (NH4)2S04.  Filter.  The 
precipitate  contains  the  albumoses,  the  filtrate  the  peptones. 
Reserve  the  filtrate  for  subsequent  tests  for  peptone.  Wash  the 
precipitate  with  a  saturated  solution  of  ammonium  sulphate; 
dissolve  in  water,  and,  with  the  solution  obtained,  perform  the 
following  tests,  noting  especially  the  tendency  of  albumose  pre- 
cipitates to  dissolve  upon  the  application  of  heat  and  to  reappear 
upon  cooling. 

Using  this  solution  of  albumose,  repeat  Exps.  187,  188,  189, 
197,  198.  If  no  precipitate  forms  with  HNO3  in  Exp.  197,  add 
a  drop  or  two  of  a  saturated  solution  of  common  salt.  (Deutero- 
albumose gives  this  reaction  only  in  the  presence  of  HCl.) 

Exp.  226.  Saturate  some  of  the  solution  with  (NH4)2S04. 
Report  the  result. 

Exp.  227.  To  some  of  the  solution  add  two  or  three  drops  of 
acetic  acid  and  then  a  saturated  solution  of  NaCl.  A  precipitate 
forms,  which  dissolves  on  heating,  and  reappears  on  cooling. 

Experiments  with  Peptones. 
Exp.  228.     Using  the  peptone  solution  prepared  in  manner 
above  described  from  commercial  peptone,  repeat  the  experi- 
ments indicated  in  Exp.  225. 


412  EXPERIMENTS 

Exp.  229.  Efect  of  Heating. — Boil  some  of  the  peptone 
solution.     Report  the  result. 

Exp.  230.  Power  of  Dialyzing.  —  Dialyze  some  of  the  peptone 
solution.  Use  10  c.c.  of  the  peptone  solution,  and  in  the  outside 
vessel  about  100  c.c.  of  water,  which  in  this  case  is  not  to  be 
changed.  After  twenty-four  hours  test  the  outside  water  for 
peptone,  employing  the  biuret  test. 

Exp.  231.  Action  of  Ammonium  Sulphate.  — Saturate  some 
of  the  peptone  solution  with  solid  (NH4)2S04.     Report  the  result. 

A  number  of  unknown  solutions  will  be  given  out  to  be 
tested  for  carbohydrates  and  proteins.  A  report  of  the  results, 
together  with  the  methods  employed,  is  to  be  made. 

Experiments  on  Blood. 

Exp.  232.  Test  the  reaction  of  blood  with  a  piece  of  litmus- 
paper  which  has  been  previously  soaked  in  a  concentrated  NaCl 
solution.     To  what  is  reaction  due? 

Exp.  233.  Blood-corpuscles.  —  {a)  Examine  a  drop  of  blood 
under  the  microscope.     Sketch  the  red  and  white  corpuscles. 

{h)  Note  the  difference  between  the  corpuscles  of  mammals 
and  those  of  birds  and  reptiles. 

(c)  Note  the  effect  upon  the  red  corpuscles  produced  by  the 
addition  of  (i)  water,  (2)  a  concentrated  solution  of  salt. 

Exp.  234.  Hemoglobin  Crystals.  —  Place  a  drop  of  de- 
fibrinated  rat's  blood  on  a  slide;  add  a  drop  or  two  of  water; 
mix,  and  cover  with  a  cover-glass.  Sketch  the  crystals  which 
separate  after  a  few  minutes.  Or  instead  of  above  add  a  few 
drops  of  ether  to  some  blood  in  a  test-tube;  shake  thoroughly 
until  the  blood  becomes  "laky,"  and  then  place  the  tube  on  ice 
till  crystals  appear. 

Exp.  235.  A  spectroscope  will  be  found  ready  for  use  in  the 
laboratory,  and  the  absorption-bands  given  by  oxyhemoglobin 
and  hemoglobin  will  be  demonstrated.  The  student  may  pre- 
pare solutions  for  examination  as  follows: 


EXPERIMENTS  ON  BLOOD  -      413 

(a)  Oxyhemoglobin.  —  Use  dilute  blood  (one  part  of  de- 
fibrinated  blood  in  fifty  parts  of  distilled  water). 

(b)  Hemoglobin  (reduced  hemoglobin) .  —  Add  to  blood  a  few 
drops  of  strong  ammonium  sulphide,  or  one  or  two  drops  of 
freshly  prepared  Stokes's  reagent.*  Note  the  change  in  color 
produced  by  the  addition  of  the  reducing  agent.  Shake  with  air 
and  note  the  rapid  change  to  oxyhemoglobin. 

(c)  Hcmochromogcn.  —  To  a  little  of  the  hemochromogen, 
reduced  with  ammonium  sulphide,  add  a  few  drops  of  concen- 
trated NaCl,  and  note  the  spectrum  of  reduced  hematin  or 
hemochromogen. 

{d)  Carbonmonoxide  Hemoglobin.  — ■  Pass  a  current  of  illumi- 
nating gas  through  a  dilute  oxyhemoglobin  solution  for  a  few 
minutes  and  filter.  Note  the  change  of  color.  Try  the  effect  on 
the  solution  of  (i)  ammonium  sulphide;  (2)  Stokes's  reagent; 
(3)  shaking  with  air.     Note  the  stability  of  the  compound. 

Exp.  236.  Take  the  specific  gravity  of  blood  by  filHng  a  test- 
tube  one-half  full  of  benzene;  add  one  drop  of  blood,  and  then 
add  chloroform,  a  drop  at  a  time,  with  careful  but  thorough  mix- 
ing, until  the  drop  of  blood  floats  at  about  the  middle  of  the 
mixture,  indicating  that  the  gravity  of  the  mixture  and  of  the 
blood  are  the  same.  The  specific  gravity  of  the  benzene  and 
chloroform  may  be  taken  in  any  convenient  way. 

Exp.  237.  Make  the  guaiacum  test  for  blood  on  a  sample 
of  dried  blood;  also  on  potato  scrapings.  The  method  is  as 
follows : 

To  a  Little  clear  solution  of  blood  or  material  obtained  from 
potato  scrapings,  add  some  fresh  tincture  of  guaiacum;  then  add 
a  few  drops  of  an  ethereal  solution  of  hydrogen  peroxide,  shake 
the  mixture  and  note  the  blue  color  obtained. 

From  these  two  tests  what  do  you  gather  about  the  value  of 

*  Stokes's  reagent  consists  of  two  parts  of  ferrous  sulphate  and  three  parts  of 
tartaric  acid  dissolved  in  water  and  ammonia  added  to  distinct  alkaline  reaction. 
There  should  be  no  permanent  precipitate. 


414  EXPERIMENTS 

the  guaiacum  test  for  blood,  and  what  is  probably  the  cause  of 
the  coloration? 

Exp.  238.  The  Benzidine  Reaction  consists  in  adding  to  a 
few  c.c.  of  a  saturated  Benzidine  solution  in  glacial  acetic  acid  or 
alcohol  acidified  with  acetic  acid  an  equal  volume  of  commercial 
H2O2  and  I  c.c.  of  the  suspected  solution.  If  blood  is  present 
a  green  or  blue  color  will  develop.  It  is  better  to  make  a  blank 
test  to  insure  purity  of  reagents. 

Exp.  239.  Hemin  Crystals  {Teichmann's  Test).  —  Place  a 
bit  of  powdered  dried  blood  on  a  glass  slide;  add  a  minute 
crystal  of  NaCl  (fresh  blood  contains  sufficient  NaCl)  and  two 
drops  of  glacial  acetic  acid.  Cover  with  a  cover-glass  and  warm 
gently  over  a  flame  until  bubbles  appear.  On  cooling,  dark- 
brown  rhombic  crystals,  often  crossed,  separate  (chloride  of 
hematin).  Similar  crystals  can  be  obtained  by  using  an  alka- 
line iodide  or  bromide  in  place  of  NaCl. 

Exp.  240.  Coagulation  of  Blood.  —  Observe  the  phenomena 
of  coagulation  as  it  takes  place  {a)  in  a  test-tube;  {h)  in  a  drop 
of  blood  examined  under  the  microscope.     Explain  fully. 

Exp.  241.  Proteins  of  Blood-plasma.  —  {a)  Serum-albumin, 
{h)  Serum-globulin.  Using  blood-serum,  separate  and  identify 
these  two  proteins. 

(c)  Fibrinogen.  —  Fibrinogen  is  a  globulin  found  in  blood- 
plasma,  lymph,  etc.,  together  with  paraglobulin.  Like  para- 
globulin  it  responds  to  all  the  general  precipitants  and  tests,  and 
in  addition  gives  the  reactions  with  COo,  dialysis,  and  MgS04. 
It  is  distinguished  from  paraglobulin  easily  by  two  reactions,  viz., 
its  power  to  coagulate,  i.e.,  to  form  fibrin  when  acted  on  by  fibrin 
ferment,  and  its  temperature  of  heat  coagulation,  which  will  be 
found  to  be  from  56°  to  60°  C. 

Exp.  242.     Fibrin.  —  {a)  Note  its  physical  properties. 

(&)    Note  action  of  0.2%  hydrochloric  acid. 

(c)   Apply  the  protein  color  tests. 


EXPERIMENTS  WITH  MUSCLE  -      415 

Experiments  with  Muscle. 

Exp.  243.  Place  25  grams  of  fresh,  finely  chopped  muscle 
in  a  beaker  with  75  c.c.  of  5%  solution  of  common  salt,  and 
allow  to  stand  for  about  one  hour,  with  frequent  stirring.  (In 
the  meanwhile  perform  Exp.  244.)  Then  filter  off  the  liquid 
and  make  the  following  tests  with  the  filtrate. 

(a)  Test  for  proteins. 

(b)  Having  found  proteins,  pour  a  little  of  the  solution  into 
a  beaker  of  water.     Result.     Inference  (myosin). 

(c)  Make  a  fractional  heat  coagulation  in  the  following  man- 
ner (upon  the  care  with  which  the  temperatures  given  are  ad- 
hered to,  depends  the  success  of  the  separation) :  Warm  to  from 
44°  to  50°  C,  and  keep  at  that  temperature  for  a  few  minutes. 
The  coagulum  is  myosin  [synonyms:  paramyosinogen  (Halli- 
burton), musculin  (older  authors)].  In  solutions  the  myosin, 
which  has  the  properties  of  a  globulin,  becomes  insoluble  after  a 
time,  because  it  changes  to  myosinfibrin.  In  heating  the  solu- 
tion as  above,  a  sHght  cloud  may  appear  at  from  30°  to  40°  C. 
This  is  due  to  coagulation  of  soluble  myogenfibrin.  Now  filter 
off  the  coagulated  myosin. 

Heat  filtrate  to  from  55°  to  65°  C.  The  coagulum  is  myogen 
(synonym:  myosinogen).  In  spontaneous  coagulation  of  its 
solutions  it  forms,  first,  soluble  myogenfibrin,  and,  finally,  in- 
soluble myogenfibrin.     Filter. 

Heat  to  from  70°  to  90°  C.  Coagulum  is  serum  albumin  from 
the  blood  within  the  muscle,  and  is  not  a  constituent  of  the 
muscle  plasma.     Filter. 

Test  filtrate  for  proteins.  If  it  shows  a  slight  biuret  test, 
this  is  due  either  to  incomplete  precipitation  by  coagulation 
or  to  the  post-mortem  formation  of  albumose  or  peptone  by 
auto-digestion  (autolysis) . 

Exp.  244.'  Make  an  aqueous  extract  of  muscle,  and  test  for 
lactic  acid  by  acidulating  with  H2SO4,  extracting  with  ether, 


41 6  EXPERIMENTS 

and  testing  the  ethereal  extract  with  very  dilute  ferric  chloride 
solution.  The  presence  of  lactic  acid  is  shown  by  a  bright- 
yellow  color. 

Experiments  with  Saliva. 

Exp.  245.  Action  of  Saliva  upon  Starch.  —  Take  some  fil- 
tered saHva  in  a  test-tube  and  place  in  the  water-bath  at  40°  C, 
for  five  or  ten  minutes.  Put  some  starch  paste  into  a  second 
test-tube  and  place  this  also  in  the  water-bath  for  a  while,  then 
mix  the  two  (10  c.c.  of  starch  paste  to  3  c.c.  of  undiluted  saHva) 
and  return  to  the  water  bath.  The  starch  is  changed  first  to 
soluble  starch  (if  originally  a  thick  paste,  it  becomes  fluid  and 
loses  its  opalescence),  then  to  erythrodextrin,  which  gives  a 
red  color  with  iodine,  and  finally  to  achroodextrin,  which  gives 
no  reaction  with  iodine,  and  to  maltose.  Prove  these  changes 
as  follows :  Every  minute  or  two  take  out  a  drop  of  the  mixture, 
place  it  on  a  porcelain  plate,  and  add  a  drop  of  iodine  solu- 
tion. This  gives  first  a  blue  color,  showing  the  presence  of 
starch;  later  a  violet  color,  due  to  the  mixture  of  the  blue  of 
the  starch  reaction  with  the  red  caused  by  the  dextrin;  next  a 
reddish-brown  color,  due  to  erythrodextrin  alone  (starch  being 
absent),  and  finally  no  reaction  at  all  with  iodine,  proving  the 
absence  of  starch  and  erythrodextrin.  The  fluid  now  contains 
achroodextrin  and  maltose.  Test  for  the  latter  with  Fehlmg's 
solution  and  with  Barfoed's  reagent. 

Exp.  246.  Influence  of  Conditions  on  Ptyalin  and  its  Amylo- 
lytic  Action. — Report  and  explain  the  results  of  the  following 
experiments: 

(a)  Boil  a  few  cubic  centimeters  of  the  saliva,  then  add 
some  starch  paste,  and  place  in  the  water  bath  at  40°  C.  After 
five  nunutes  test  for  sugar. 

(6)  Take  two  test-tubes:  put  some  starch  paste  in  one,  and 
saHva  in  the  other,  and  cool  them  to  0°  C,  in  a  freezing  mixture. 
Mix  the  two  solutions,  and  keep  the  mixture  surrounded  by 


ANALYSIS  OF  GASTRIC  CONTENTS  ,  417 

ice  for  several  minutes,  then  test  a  portion  for  sugar.  Now 
place  the  remainder  in  the  water  bath  at  40°  C,  and  after  a 
time  test  for  sugar. 

(c)  Carefully  neutralize  20  c.c.  of  saliva  with  very  dilute 
HCl  (the  0.2%  diluted),  and  dilute  the  whole  to  100  c.c.  Test 
the  action  of  this  neutralized  saliva  on  starch. 

(d)  To  5  c.c.  of  starch  paste  add  10  c.c.  of  0.2%  HCl  and 
5  c.c.  of  neutral  saliva,  and  expose  the  mixture  for  a  while  at 
40°  C,  and  test  for  sugar. 

(c)  To  5  c.c.  of  starch  paste  add  10  c.c.  of  a  0.5%  solution 
of  Na2C03  and  5  c.c.  of  neutral  saliva,  and  expose  the  mixture 
for  a  while  at  40°  C,  and  test  for  sugar. 

(J)  Carefully  neutralize  {d)  and  (e) ,  and  again  test  the  action 
of  the  two  on  starch. 

(g)  Mix  a  little  uncooked  starch  with  saliva,  expose  to  a 
temperature  of  40°  C.  for  a  while,  and  test  for  sugar. 

Exp.  247.  In  three  separate  test-tubes  place  a  few  cubic 
centimeters  of  dilute  solutions  of  KCNS  or  NH4CNS,  of  meconic 
acid,  and  of  acetic  acid;  add  to  each  a  few  drops  of  ferric  chloride, 
and  notice  that  a  similar  color  is  obtained  in  each  case.  Divide 
the  contents  of  each  tube  into  two  portions,  and  to  one  set  add 
HCl;  to  the  other  add  mercuric-chloride  solution.  Formulate  a 
method  of  distinguishing  from  the  sulphocyanates,  meconates, 
and  acetates. 

Analysis  of  Gastric  Contents  and  Experiments  with  Pepsin. 

The  following  solutions  will  be  found  in  the  laboratory: 

A.  A  0.2%  Solution  of  HCl.  — This  is  prepared  by  diluting 
6.5  c.c.  of  concentrated  HCl  (sp.  gr.  1.19)  with  distilled  water 
to  I  liter. 

B.  A  Solution  of  Pepsin. — Prepared  by  dissolving  two 
grams  of  pepsin  in  1000  c.c.  of  water. 

C.  A  Pepsin-hydrochloric-acid  Solution.  —  Prepared  by  dis- 
solving two  grams  of  pepsin  in  1000  c.c.  of  solution  A. 


4i8  EXPERIMENTS 

Or,  add  to  150  c.c.  of  solution  A  about  10  c.c.  of  the  glyc- 
erol extract  of  the  mucous  membrane  of  the  stomach. 

Exp.  248.  Take  five  test-tubes  and  label  a,  b,  c,  d,  e.  Fill 
as  indicated  below.  Place  in  a  water  bath  at  40°  C,  and  ex- 
amine an  hour  later,  and  again  the  next  day. 

(a)  3  c.c.  pepsin  solution  +  10  c.c.  water  +  a  few  shreds  of 
fibrin. 

(b)  10  c.c.  0.2%  HCl  -f  a  few  shreds  of  fibrin. 

(c)  3  c.c.  pepsin  solution  +  10  c.c.  0.2%  HCl,  and  a  few 
•  shreds  of  fibrin. 

(d)  3  c.c.  pepsin  solution  -|-  10  c.c.  0.2%  HCl,  boil,  and  then 
add  a  few  shreds  of  fibrin. 

(e)  3  c.c.  pepsin  solution  +  10  c.c.  0.2%  HCl,  and  a  few 
shreds  of  fibrin  which  have  been  tied  firmly  together  into  a  ball 
with  a  thread. 

Make  a  note  of  all  changes. 

Exp.  249.  Filter  c.  Neutralize  with  dilute  Na2C03.  Filter 
again.     Why?     Test  the  filtrate  for  the  biuret  reaction. 

Exp.  250.  To  5  grams  fibrin  add  30  c.c.  of  the  pepsin  solu- 
tion and  100  c.c.  0.2%  HCl.  Set  in  the  water  bath  at  40°  C, 
stirring  frequently,  and  leave  in  the  water  bath  overnight. 
Observe  the  undigested  residue,  on  the  following  day,  and  also 
a  slight  flocculent  precipitate.     What  is  this  precipitate? 

Filter  and  carefully  neutralize  the  filtrate.  A  precipitate 
varjdng  with  the  progress  of  the  digestion  will  form.     What  is  it? 

Remove  this  by  filtration,  and  saturate  this  filtrate  with 
(NH4)2S04.  Filter.  Save  precipitate  and  filtrate.  Of  what 
does  each  consist? 

Exp.  251.  Dissolve  the  last  precipitate  of  Exp.  250  in  water, 
and  try  the  following  tests: 

(a)  Biuret  reaction. 

(b)  Effect  of  boiling. 

(c)  Test  with  NHO3,  as  in  performing  test  for  albumin  in  the 
urine,  page  344. 


ANALYSIS  OF  GASTRIC  CONTENTS  419 

Exp.  252.  To  the  last  tiltrate  of  Exp.  250  add  an  equal  vol- 
ume of  95%  alcohol,  and  stir  thoroughly.  The  peptones  will 
collect  in  a  gummy  mass  about  the  stirring-rod. 

(a)  Determine  the  solubility  of  peptones  in  water. 

(b)  What  is  the  effect  of  heat  when  so  dissolved? 

(c)  Try  the  biuret  reaction. 

Exp.  253.  Demonstration  of  Rennet  Enzyme.  — Place  10  c.c. 
of  milk  in  each  of  three  test-tubes.     Label  the  test-tubes  i,  2,  3. 

To  I  add  a  drop  of  neutralized  glycerol  extract  of  the  mucous 
membrane  of  the  stomach  (made  from  the  stomach  of  the  calf). 

To  2  add  a  drop  of  neutralized  glycerol  extract,  and  boil 
at  once. 

To  3  add  a  few  cubic  centimeters  of  (NH4)2C204  solution, 
and  then  a  drop  of  a  glycerol  extract. 

Place  these  tubes  in  the  water  bath  at  40°  C,  and  examine 
after  five  to  ten  minutes.     Explain  results  in  each  case. 

Continue  heating  tube  3  for  half  an  hour,  then  add  2  or  3 
drops  CaCli  solution.     The  liquid  instantly  solidifies.     Why? 

Exp.  254.  Digestion  of  Casein.  —  Determine  the  products  of 
the  digestion  of  the  curd  from  the  last  experiment. 

Exp.  255.  Tests  for  Free  Hydrochloric  Acid.  —  Try  each 
of  the  following  tests  with  (a)  HCl  (0.2%,  0.05%,  and  0.01% 
successively);  (b)  lactic  acid  (1%);  (c)  mixtures  containing 
equal  volumes  of  (a)  and  (b).     Tabulate  the  results. 

{a)  Dimethylaminoazobenzene.  —  Use  one  or  two  drops  of  a 
0.5%  alcoholic  solution.  In  the  presence  of  free  mineral  acids 
a  carmine-red  color  is  obtained. 

(b)  Gunzburgs  Reagent.  —  Phloroglucin,  2  grams ;  vanilhn, 
I  gram;  alcohol,  100  c.c.  Place  two  or  three  drops  of  the  solu- 
tion to  be  tested  in  a  porcelain  dish,  add  one  or  tw^o  drops  of 
the  reagent,  and  evaporate  on  a  water  bath.  In  the  presence 
of  free  hydrochloric  acid  a  rose-red  color  develops. 

(c)  Boas'  Reagent.  -^  This  is  prepared  by  dissohing  5  grams 
of  resublimed  resorcinol  and  a  gram  of  cane-sugar  in  100  grams 


420  EXPERIMENTS 

of  94%  alcohol.  Take  three  or  four  drops  each  of  the  reagent 
and  the  solution  to  be  tested,  and  cautiously  evaporate  to 
dryness.  In  the  presence  of  a  free  mineral  acid  a  rose  or  ver- 
miUion  red  color  is  obtained.     This  gradually  fades  on  cooling. 

{d)  Tropccolin  00.  —  Use  one  or  two  drops  of  a  saturated 
alcoholic  solution. 

(e)  Congo-red.  —  Use  filter-paper  which  has  been  dipped  into 
a  solution  of  the  reagent  and  then  dried. 

Exp.  256.  To  5  c.c.  egg-albumin  in  solution  add  i  c.c.  of 
0.2%  HCl.  Mix  thoroughly,  and  test  for  the  presence  of  free 
HCl.  What  is  the  result?  How  do .  you  explain  it?  Repeat 
the  test,  using  a  solution  of  peptone  in  place  of  the  egg-albumin. 

Exp.  257.  Tests  for  Lactic  Acid. — ^Uffelmann's  reagent. 
Mix  10  c.c.  of  a  4%  solution  of  carbolic  acid  with  20  c.c.  of 
water,  and  add  a  drop  or  two  of  ferric  chloride. 

To  5  c.c.  of  the  reagent  add  a  few  drops  of  the  lactic-acid 
solution.     Note  the  canary-yellow  color. 

Does  the  presence  of  free  HCl  interfere  with  this  reaction? 

A  more  delicate  reagent  is  obtained  by  adding  three  or  four 
drops  of  a  10%  ferric-chloride  solution  to  50  c.c.  of  water.  Such 
a  solution  has  a  very  faint  yellow  color,  which  is  distinctly  in- 
tensified by  lactic  acid. 

Using  5  c.c.  of  this  nearly  colorless  solution  for  each  experi- 
ment, note  the  effect  of  (a)  0.2%  HCl;  (b)  acid  phosphate  of 
sodium;  (c)  alcohol;  (d)  glucose;  (e)  cane-sugar.  What  con- 
clusions do  you  reach  concerning  the  value  of  this  test,  when 
applied  directly  to  the  gastric  contents? 

The  test  is  best  applied  to  an  aqueous  solution  of  the  ethereal 
extract  of  the  gastric  contents.  Add  to  the  contents  two  drops 
of  HCl,  boil  to  a  syrup,  and  extract  with  ether.  Dissolve  the 
residue  obtained  upon  evaporation  of  the  ether  in  a  little  water, 
and  test  for  lactic  acid. 

Exp.  258.    Test  for  butyric  acid;  see  ethyl  butyrate,  page  215. 

Exp.  259.     Test  for  acetic  acid;  see  acetates  (page  100). 


EXPERIMENTS   WITH   PANCREATIC  JUICE  '      42 1 

Exp.  260.  The  acidity  of  the  gastric  contents  may  be  deter- 
mined as  follows:  To  5  c.c.  of  the  filtered  contents,  diluted  with 
25  to  30  c.c.  of  water  in  an  Erlenmeyer  flask,  add  2  or  3  drops 
of  a  solution  of  dime  thy  laminoazobenzene.  Titrate  with  N/io 
alkali  till  the  color  changes  to  a  yellow  which  fairly  matches 
the  indicator;  this  represents  the  free  HCl.  To  this  mixture 
add  a  few  drops  of  phenolphthalein  solution,  and  continue  the 
titration  until  a  permanent  pink  color  is  obtained.  The  N/io 
alkah  used  will  represent  the  total  acidity,  combined  HCl,  and 
organic  acids.  The  organic  acids  will  not  be  present  in  gastric 
contents  in  the  presence  of  any  appreciable  amount  of  free 
HCl,  as  they  are  derived  almost  entirely  from  fermentations 
which  are  inhibited  by  the  hydrochloric  acid. 

Experiments  with  Pancreatic  Juice. 

Exp.  261.  Proteolytic  Action.  —  To  25  c.c.  of  a  1%  solution 
of  Na2C03  add  a  few  drops  of  the  pancreatic  extract.  Place 
some  pieces  of  fibrin  in  this  Hquid,  and  keep  in  the  water  bath 
at  40°  C.  till  the  fibrin  has  disappeared  (one  or  two  hours  prob- 
ably). Observe  the  digestion  from  time  to  time.  Note  that 
the  fibrin  does  not  swell  and  dissolve  as  in  gastric  digestion,  but 
that  it  is  eaten  away  from  the  edges. 

Filter.  What  is  the  precipitate?  Carefully  neutralize  the 
filtrate  with  0.2%  HCl.  Another  precipitate  may  appear. 
What  is  this? 

Again  filter,  if  necessary,  and  test  the  filtrate  for  proteoses 
and  peptones  as  directed  under  gastric  digestion. 

Exp.  262.  Amylolytic  Action.  —  To  some  starch  paste  in  a 
test-tube  add  a  drop  or  two  of  the  pancreatic  extract  and  place 
in  the  water  bath  at  40°  C.  After  a  few  minutes  test  for  sugar 
and  report  the  result. 

Exp.  263.  The  Piolytic  {Fat-splitting)  Action.  —  For  the 
demonstration  of  this  action  use  natural  pancreatic  juice,  or 
finely  divided  fresh  pancreas,  or  a  recently  prepared  extract. 


422  EXPERIMENTS 

To  some  perfectly  neutral  olive  oil,  colored  faintly  blue 
with  litmus,  add  half  its  volume  of  the  pancreatic  extract, 
shake  thoroughly,  and  keep  at  40°  C.  for  twenty  minutes. 
Record  the  result.     Reserve  for  next  experiment. 

Exp.  264.  Emulsifying  Action.  — To  10  c.c.  of  a  0.2%  solu- 
tion of  Na'jCOa  add  a  few  drops  of  the  mixture  used  in  Exp.  263. 
Shake  thoroughly,  and  report  the  result.  Referring  to  the 
earlier  experiments  on  emulsification  (see  Fats),  explain  the 
efficacy  of  the  pancreatic  juice  in  emulsifying  fats. 

Experiments  with  Bile. 

Exp.  265.  Color.  —  Note  the  difference  in  color  between 
human  bile  and  ox  bile.     Explain. 

Exp.  266.  Reaction.  —  Dilute  some  bile  with  four  parts  of 
water.  Immerse  a  strip  of  red  litmus  paper,  then  remove  and 
wash  with  water.     Note  the  reaction. 

Exp.  267.  Nucleo-albumin.  —  Dilute  bile  with  twice  its 
volume  of  water,  filter  if  necessary,  and  add  acetic  acid.  What 
is  the  precipitate?     How  distinguished  from  mucin? 

Exp.  268.  Filter  267  and  test  the  filtrate  for  proteins. 
Report  the  result. 

Exp.  269.  Separation  of  Bile  Salts.  —  Mix  20  c.c.  of  bile 
with  animal  charcoal  to  form  a  thick  paste,  and  evaporate  on  the 
water  bath  to  complete  dryness.  Pulverize  the  residue  in  a 
mortar,  transfer  to  a  flask,  add  25  c.c.  of  absolute  alcohol,  and 
heat  on  the  water  bath  for  half  an  hour.  Filter.  To  the  fil- 
trate add  ether  till  a  permanent  precipitate  forms.  Let  the 
mixture  stand  for  a  day  or  two,  and  then  filter  off  the  crystalline 
deposit  of  bile  salts.  Save  the  filtrate  which  contains  choles- 
terin.     (Plate  VII,  Fig.  4,  page  287.) 

Exp.  270.  Bile-pigments.  —  (a)  Gmelin^s  Test.  —  Take  some 
bile  in  a  wine-glass  and  underlay  with  yellow  HNO3,  in  the 
manner  described  in  testing  saliva  for  albumin.  Notice  the 
play  of  colors,  beginning  with  green  and  passing  through  blue, 


EXPERIMENTS   WITH   BILE  '         423 

violet,  and  red  to  yellow,  at  the  junction  of  the  two  liquids. 
Explain. 

{h)  Iodine  Test.  —  Place  10  c.c.  of  dilute  bile  in  a  test-tube, 
and  add  slowly  two  or  three  cubic  centimeters  of  dilute  tincture 
of  iodine,  so  that  it  forms  an  upper  layer.  A  bright  green  ring 
forms  at  the  Hne  of  contact. 

Exp.  271.  Cholesterol.  —  Examine  under  the  microscope  the 
crystals  obtained  by  the  cautious  evaporation  of  the  alcohol- 
ether  filtrate  of  Exp.  269. 

Concentrated  H2SO4,  containing  a  little  iodine,  gives  with 
cholesterol  a  series  of  colors  passing  from  violet  to  blue,  then  to 
green  and  finally  red. 

Exp.  272.  Action  of  Bile  in  Digestion.  —  (a)  Take  three 
test-tubes.  In  one  mix  10  c.c.  of  bile  and  2  c.c.  of  neutral  olive 
oil;  in  the  second,  10  c.c.  of  bile  and  2  c.c.  of  rancid  olive  oil; 
in  the  third,  10  c.c.  of  water  and  2  c.c.  of  neutral  oil.  Shake  and 
place  in  a  water  bath  at  40°  C.  for  some  time.  Note  the  extent 
and  the  permanency  of  the  emulsion  in  each  case. 

(h)  Into  each  of  two  funnels  fit  a  filter-paper.  Moisten  one 
with  water  and  the  other  with  bile,  and  into  each  pour  an  equal 
volume  of  olive  oil.  Set  aside  for  twelve  hours  (with  a  beaker 
under  each  funnel).  Do  you  notice  any  difference  in  the  rate 
of  filtration? 

(c)  Add  drop  by  drop  a  solution  of  bile  salts  to  (a)  a  solution 
of  egg-albumin;  {b)  a  solution  of  acid-albumin;  (c)  a  solution 
obtained  by  digesting  a  bit  of  fibrin  in  gastric  juice  and  filtering. 
Explain  the  results. 


APPENDIX. 
REAGENTS. 


It  is  desirable  that  all  reagents  be  made  with  reference  to  the 
molecular  weights  of  the  substances  employed.  These  may  be 
from  one  to  ten  times  the  molecular  weight  per  liter,  while  the 
solutions  for  practice  are  from  one-tenth  to  one-fourth  the 
molecular  weight  per  liter.  Salt  solutions  used  as  reagents  are 
conveniently  from  five  to  ten  per  cent. ;  that  is,  a  molar  concen- 
tration is  selected  bringing  the  strength  within  these  limits. 

In  the  following  list  a  few  exceptions  will  be  noted. 

Ammonia  (dilute).  —  Strong  ammonia  one  part,  distilled 
water  two  parts. 

Ammonium  Carbonate,  2M;  157  grams  of  commercial 
ammonium  carbonate  are  dissolved  by  the  aid  of  heat  in  about 
900  c.c.  water.  After  this  has  become  cold  add  75  c.c.  of  con- 
centrated ammonium  hydroxide,  and  make  up  volume  to  one 
liter. 

Ammonium  Chloride,  4M,  or  about  a  twenty  per  cent, 
solution. 

Ammoniacal  Cuprous  Chloride  may  be  made  by  dissolving 
copper  oxide  with  metallic  copper  in  dilute  hydrochloric  acid 
with  the  aid  of  heat.  To  the  clear,  cool,  resulting  solution  add 
ammonia  to  marked  alkaline  reaction. 

Ammonium  Molybdate  Solution  for  Phosphates.  —  This  may 
be  made  by  dissolving  twenty  grams  of  ammonium  molybdate  in 
a  mixture  of  250  c.c.  NH4OH  and  250  c.c.  of  water.  Then  this 
solution  is  added  to  1000  c.c.  of  nitric  acid  making  1500  c.c.  of 
reagent.     In  using  this  solution  as  a  test  for  phosphates  it  is 

necessary  to  heat  the  mixture  to  about  60°  C. 

424 


REAGENTS  425 

If  the  reagent  is  prepared  as  follows  it  reacts  without  heating, 
is  more  sensitive  than  that  produced  by  the  tirst  formula  and  is 
recommended  as  the  better  of  the  two.  Dissolve  100  grams  of 
mol}bdenum  trioxide  (molybdic  acid)  in  400  c.c.  of  dilute  NH4OH 
(10^).  Allow  to  cool  and  add  all  at  once  1000  c.c.  of  dilute 
HNOsCHXOs  three  parts,  H2O  two  parts).  The  precipitate  first 
formed  is  immediately  redissolved  and  the  product  should  be 
a  perfectly  clear,  nearly  colorless  solution. 

Ammonium  oxalate,  ]\I  4,  35.52  grams  per  Kter. 

Ammoniacal  Silver  Solution.  —  Dissolve  10  grams  of  silver 
nitrate  in  200  c.c.  of  water  and  add  about  50  c.c.  of  strong 
ammonia,  or  an  amount  considerably  in  excess  of  that  required 
to  dissolve  the  precipitate  lirst  formed. 

Ammonium  Sulphide.  —  Saturate  300  c.c.  of  strong  arnmonia 
with  hydrogen  sulphide  gas.  Then  add  an  equal  volume  of 
strong  ammonia  and  sufficient  water  to  make  1000  c.c.  In  this 
solution  dissolve  one  or  two  grams  of  sulphur,  giving  the  yellow 
or  ammonium  sulpliide  (polysulphide) . 

Barium  Chloride,  BaClo.2  HoO,  M/2,  or  122.16  grams  per  liter. 

Barfoed's  Reagent.  —  Dissolve  one  part  of  copper  acetate 
in  fifteen  parts  of  water;  to  each  200  c.c.  of  this  solution  add 
5  c.c.  of  acetic  acid  containing  thirty-eight  per  cent,  of  glacial 
acetic  acid. 

Benedict's  Solution  has  the  follomng  composition: 

Gm.  or  c.c. 

Copper  sulphate  (pure  cn-stallized) 17.3 

Sodium  or  potassium  citrate 1730 

Sodium  carbonate  (crystallized) 200 .  o 

or  one-half  the  weight  of  the  anhydrous  salt 
Distilled  water  to  make 1000 .  o 

The  citrate  and  carbonate  are  dissolved  together  (^\•ith  the  aid 
of  heat)  in  about  700  c.c.  of  water.  The  mixture  is  then  poured 
(through  a  filter  if  necessary)  into  a  larger  beaker  or  casserole. 
The  copper  sulphate  (which  should  be  dissolved  separately  in 


426  APPENDIX 

about  loo  c.c.  of  water)  is  then  poured  slowly  into  the  first 
solution  with  constant  stirring.  The  mixture  is  then  cooled  and 
diluted  to  one  hter.* 

Benzidine  Solution.  —  Saturated  solution  of  benzidine  in 
glacial  acetic  acid  with  an  equal  volume  of  peroxide  of  hydrogen 
solution.  The  two  solutions  are  to  be  mixed  when  used  as  a  test 
for  blood. 

The  following  method  of  making  the  benzidine  solution  is 
suggested  by  Hawk's  Physiological  Chemistry:  4.33  c.c.  of  glacial 
acetic  add  is  warmed  in  a  small  Erlenmeyer  flask  to  about  50°  C, 
a  half  gram  of  benzidine  added,  and  the  mixture  heated  eight 
or  ten  minutes  at  50°  C.  and  then  the  solution  diluted  with  19  c.c. 
of  distilled  water.     If  kept  in  a  dark  place  it  is  fairly  permanent. 

Congo  Red.  —  Two  per  cent,  aqueous  solution. 

CUSO4  Solution.  —  One  per  cent,  for  Biuret  test. 

Dimethyl-amino-azobenzene. — 0.5  per  cent,  alcoholic  solution. 

Esbach's  Reagent.  —  Picric  acid  ten  grams,  and  citric  acid 
20  grams  dissolved  in  sufficient  water  to  make  one  liter  of  solution. 

Fehling's  Solution.  —  The  FehHng's  solution  recommended 
for  experiments  in  this  book  is  one-half  the  strength  frequently 
employed,  and  is  prepared  in  separate  solutions  as  follows: 
Dissolve  34.639  grams  of  pure  crystallized  copper  sulphate  in 
water,  and  make  solution  up  to  one  Hter.  This  constitutes  the 
first  part  of  the  reagent.  The  second  part  may  be  made  by 
dissolving  173  grams  of  Rochelle  salts  and  52.7  grams  of  caustic 
soda  (NaOH)  in  water  and  making  up  to  one  liter.  When  pre- 
pared in  this  way  10  c.c.  of  each  of  these  solutions  mixed  to- 
gether will  be  reduced  by  0.05  gram  of  glucose. 

Ferric  Chloride.  —  2.5  per  cent,  solution  acidified  with  HCl. 

Goulard's  Extract  is  a  solution  of  lead  subacetate,  q.v. 

Gram's  Solution.  —  See  iodine  solution. 

Gunzburg's  Reagent.  —  Phloroglucin,  2  grams;  vanillin,  i 
gram;  alcohol,  100  c.c. 

*  Jour.  Amer.  Med.  Assoc,  Oct.  7,  1911,  p.  1193. 


REAGENTS  427 

Hopkins-Cole  Reagent,  glyoxylic  acid,  CHO.COOH.HoO,  is 
prepared  by  saturating  a  liter  of  water  with  oxalic  acid,  adding 
sixty  grams  of  sodium  amaJgam  and  allowing  to  stand  until 
reduction  is  complete  or  until  hydrogen  ceases  to  be  evolved. 
For  use  this  solution  should  be  filtered  and  diluted  with  two  or 
three  volumes  of  water. 

Hydrochloric  Acid  (dilute).  —  Hydrochloric  acid,  strong, 
(sp.  gr.  1.20)  one  part;   distilled  water,  two  parts. 

Hypobromite  Solution  for  Urea.  —  Consists  of  a  mixture  of 
equal  parts  of  the  following  solutions  kept  separately  and  mixed 
for  use: 

Bromine  Solution  for  Urea.  — 12^  grams  KBr  and  125  grams 
Br  to  one  Hter  water. 

NaOH  Solution  Jar  Urea.  —  A  40  per  cent,  solution,  or  a  ten 
molar  solution. 

Iodine  Solution.  —  10  grams  iodine,  20  grams  KI,  made  up 
with  wkter  to  one  liter. 

Iodine  Tincture.  —  See  tincture. 

Invertase.  —  MLx  500  gms.  of  "  beer  yeast,"  200  c.c,  of  water 
and  10  gms.  of  sugar,  allow  to  stand  one  hour.  Add  50  c.c.  of 
60%  alcohol  and  a  Httle  thymol.  Filter,  press  or  allow  to  dry, 
put  the  nearly  dry  mass  in  a  flask,  add  twenty  gms.  of  sugar  and 
shake  till  solution  is  effected.     Keep  in  ice  chest. 

If  "beer  yeast"  is  not  available  a  solution  of  invertase,  rather 
less  satisfactory  than  the  above,  can  be  made  as  follows:  Take 
one  dozen  compressed  yeast  cakes,  grind  with  sand  and  mix 
wdth  500  c.c.  of  water,  and  a  httle  chloroform  as  preservative. 
AUow  to  stand  twelve  hours  and  filter. 

Iodine  Solution.  — 

LugoVs  solution  is  iodine  five  grams,  potassium  iodide  ten 
grams,  and  sufficient  distilled  w^ater  to  make  one  hundred  grams. 
(U.S.  P.) 

Grant's  solution:  Iodine  one  gram,  potassium  iodide  two 
grams,  and  sufficient  distilled  water  to  make  two  hundred  grams. 


428  APPENDIX 

Lead  Subacetate,  or  basic  acetate  of  lead.  The  U.  S.  P. 
method  of  preparation  is  as  follows:  lead  acetate  i8o  grams,  lead 
oxide  no  grams,  distilled  water  to  make  looo  grams.  Rub  lead 
oxide  to  a  paste  with  loo  c.c.  of  water,  dissolve  lead  acetate  in 
700  c.c.  of  boiling  distilled  water;  add  slowly  with  constant 
stirring  to  lead  oxide  and  boil  the  mixture  for  half  an  hour. 
Cool  and  filter  and  make  up  to  1000  c.c.  with  water  free  from 
carbon  dioxide. 

Leucin.  —  See  under  Cystin,  page  432. 

Lipase.  —  From  castor  bean  (see  page  399).  Remove  the 
shells  from  ten  grams  of  fresh  beans,  break  them  up  as  fine  as 
possible  and  allow  to  stand  overnight  in  a  loosely  stoppered  test- 
tube  full  of  alcohol  ether  mixture.  Pour  off;  grind  the  beans  to 
a  powder  in  a  small  mortar,  transfer  to  a  test-tube  and  let  stand 
under  ether  overnight.  Filter  with  suction  and  wash  two  or 
three  times  with  small  amounts  of  the  alcohol  ether  mixture. 

Lipase.  —  From  pancreas.  Take  a  pig's  pancreas,  remove 
all  fat,  grind  and  allow  to  stand  overnight.  Then  add  four 
times  its  weight  of  25%  alcohol  and  allow  to  stand  three  days. 
Syphon  off  clear  fluid  and  neutralize  with  sodium  carbonate. 
The  solution  will  contain  a  fat-spHtting  enzyme. 

Lugol's  Solution.  —  See  Iodine. 

Magnesia  Mixture.  —  125  grams  of  ammonium  chloride, 
125  grams  of  magnesium  sulphate,  dissolved  in  sufficient  water 
to  make  one  Hter  of  solution,  then  add  125  c.c.  of  strong  am- 
monia water. 

Marme's  Reagent.  —  10  grams  potassium  iodide,  5  grams 
cadmium  iodide,  100  c.c.  water. 

Mercuric  Chloride  Solution.  —  Five  per  cent.  HgCl2  in  dis- 
tilled water. 

Millon's  Reagent.  —  To  one  part  of  mercury  add  two  parts 
nitric  acid  of  specific  gravity  1.4,  and  heat  on  the  water  bath 
till  the  mercury  is  dissolved.  Dilute  with  two  volumes  of  water. 
Let  the  precipitate  settle,  and  decant  the  clear  fluid. 


REAGENTS  -      429 

Molisch's  Reagent  for  Carbohydrates.  —  Fifteen  per  cent, 
solution  of  a-naphthol  in  alcohol. 

Nessler's  Solution. — -An  alkaline  solution  of  potassio-mercuric 
iodide,  made  as  follows:  Dissolve  35  grams  of  potassium  iodide  in 
about  200  c.c.  of  water.  Dissolve  17  grams  of  mercuric  chloride 
in  300  c.c.  of  hot  water.  Add  the  potassium  iodide  to  the  mer- 
curic chloride,  until  the  precipitate  at  first  formed  is  nearly  all 
redissolved.  If  the  precipitate  should  entirely  dissolve,  add  a  few 
cubic  centimeters  of  a  saturated  solution  of  mercuric  chloride, 
until  a  slight  permanent  precipitate  is  obtained.  After  the 
mixture  is  cold,  make  up  to  one  liter  with  a  twenty  per  cent, 
solution  of  caustic  potash.  Allow  to  settle  and  use  the  clear 
solution. 

Nitric  Acid  (dilute).  —  Strong  HNO3  (sp.  gr.,  1.42)  one  part, 
and  water  three  parts. 

Pancreatic  Extract.  —  Obtain  a  fresh  pancreas  and  soak  in 
four  times  its  weight  of  25%  alcohol  for  two  or  three  days. 
Filter  and  make  the  solution  neutral  or  very  slightly  alkaline 
with  sodium  carbonate.  This  solution  will  contain  the  fat- 
splitting  enzyme. 

Phenoldisulphonic  Acid.  —  Phenoldisulphonic  acid,  for  esti- 
mation of  nitrates  in  water  analysis,  may  be  prepared  by  heat- 
ing on  a  water  bath  for  several  hours  a  mixture  of  555  grams  of 
concentrated  sulphuric  acid  and  45  grams  of  pure  carbolic-acid 
crystals. 

Phenyl-hydrazine  Solution.  —  One  gram  phenyl-hydrazine 
hydrochloride  and  two  grams  sodium  acetate  dissolved  in  10  c.c. 
water. 

Picric-acid  Solution  (Esbach's  Reagent).  —  Picric  acid,  ten 
grams;  citric  acid,  twenty  grams;  dissolved  in  sufficient  water  to 
make  one  liter. 

Potassium  Ferrocyanide  Solution.  —  K4Fe(CN)6,  one-fourth 
molar  solution  (9.2%). 

Schiff's  Reagent.  —  Into  50  c.c.  of  a  2  per  cent,  solution  of 


430  APPENDIX 

Fuchsine  or  Rosaniline  pass  SO2  gas  until  the  solution  is  colorless. 
Then  dilute  with  an  equal  volume  of  water  and  keep  in  small  full 
bottles  in  a  dark  place. 

Silver-nitrate  Solution.  —  Drop  solution,  i  :  8,  used  as  a 
quahtative  test  for  chlorine  in  urine. 

Quantitative  Solution  for  Chlorine  Titration  in  Urine.  —  29.075 
grams  silver  nitrate,  made  up  to  one  liter  with  water,  i  c.c.  of 
this  solution  corresponds  to  0.0 1  gram  sodium  chloride  or  0.00607 
gram  chlorine,  or  a  N/io  silver  nitrate  solution  may  be  used,  one 
c.c.  of  which  will  be  equivalent  to  0.00355  gram  of  chlorine. 

Starch  Paste  (thin).  —  Rub  about  one-half  gram  of  starch  to 
a  thin  paste  with  cold  water.  Add  sufficient  boiling  water  to 
dissolve,  then  dilute  to  100  or  150  c.c. 

Sulphuric  Acid  (dilute).  —  Twenty  per  cent,  strong  H2SO4  in 
distilled  water. 

Tincture  Iodine  for  Bile  Test.  —  Dilute  the  U.  S.  P.  tincture 
with  alcohol  until  just  transparent  in  test-tube. 

Tollen's  Reagent.  —  Make  a  10  per  cent,  solution  of  AgNOs  in 
dilute  ammonia  and  just  before  using  mix  an  equal  volume  of 
this  solution  with  a  10%  solution  of  NaOH. 

Tropaeolin  00.  —  Saturated  alcoholic  solution. 

Uffelmann's  Reagent. — -Mix  10  c.c.  of  a  four  per  cent,  solution 
of  carbolic  acid  with  20  c.c.  of  water,  and  add  a  drop  or  two  of 
ferric  chloride. 

PREPARATIONS. 

Creatin  may  be  most  conveniently  prepared  from  a  strong 
solution  of  Liebig's  extract.  Dissolve  the  extract  in  twenty 
parts  of  water,  add  basic  lead  acetate  drop  by  drop  to  avoid  more 
than  a  slight  excess,  then  remove  excess  of  lead;  concentrate  to 
a  syrup  over  a  water  bath  and  allow  to  stand  in  a  cool  place, 
when  creatin  crystals  will  separate  out.  Two  or  three  days' 
time  may  be  required  before  the  crystals  are  obtained.  They 
may  be  washed  with  88%  alcohol  and  purified  by  recrystalliza- 


PREPARATIONS  ,        431 

tion  from  water.  Hypoxanthin  and  sarcolactic  acid  may  be 
obtained  from  the  mother  liquor,* 

Creatinin  may  be  prepared  from  creatin  by  boiling  for  ten  or 
fifteen  minutes  with  very  dilute  sulphuric  acid.  Neutralize  the 
acid  with  BaCOs,  filter,  evaporate  to  dryness  on  a  water  bath, 
and  extract  the  creatinin  with  alcohol.  Upon  evaporation  the 
creatinin  is  obtained  in  the  form  of  crystals. 

Cystin.  —  i.  Clean  200  grams  of  hair  by  washing  with  dilute 
HCl  and  then  with  ether.  Boil  the  clean  hair  with  600  c.c.  of  con- 
centrated HCl  (specific  gravity,  1.19)  for  four  hours  (in  a  three- 
liter  flask  with  condenser)  an  a  sand-bath  in  hood.    Then  let  cool. 

2.  Add  concentrated  NaOH  solution  (750  c.c.  HoO,  500 
grams  NaOH)  till  the  reaction  is  only  faintly  acid. 

3.  Add  to  the  solution,  which  has  begun  to  boil  on  neu- 
tralization, plenty  of  animal  charcoal,  and  boil  three-quarters 
of  an  hour. 

4.  Filter  hot,  being  careful  to  moisten  filter  and  funnel  with 
hot  water  to  prevent  funnel  from  cracking. 

5.  The  filtrate  should  be  faintly  yellow.  On  cooling,  a 
crystalHne  precipitate  forms,  mainly  cystin,  with  some  tyrosin 
and  leucin.  If  this  is  not  the  case,  or  if  the  precipitate  is  sHght, 
the  solution  must  be  concentrated.  Save  the  filtrate,  which  with 
the  filtrate  from  6  is  to  be  worked  up  later  for  tyrosin  and  leucin. 

6.  After  standing  overnight  filter  off  the  precipitate. 

7.  Dissolve  this  precipitate  in  350  c.c.  of  hot  10  per  cent. 
NH4OH  (hood)  and  let  cool.  Then  continue  the  cooKng  with 
finely  chopped  ice  or  with  snow.  Filter  oft'  any  t>TOsin  that 
may  have  precipitated,  and  combine  it  with  the  filtrate  of  6. 

8.  Add  glacial  acetic  acid,  being  careful  not  to  acidify.  The 
precipitate  is  a  mixture  of  tyrosin  and  cystin.     Filter. 

9.  Make  filtrate  from  8  quite  acid  with  glacial  acetic  acid. 
The  precipitate  is  almost  pure  cystin.  Let  stand  twenty-four 
hours.     Then  filter,  and  wash  with  HoO  and  alcohol. 

*  Lea's  Chemical  Basis  of  the  Animal  Body. 


432  APPENDIX 

lo.  Recrystallize  by  redissolving  in  as  little  hot  lo  per  cent, 
ammonia  as  is  necessary  to  effect  solution,  cooling  and  precipitat- 
ing with  glacial  acetic  acid. 

The  preparations  should  be  pure  and  contain  no  tyrosin, 
for  which  test  may  be  made  with  Millon's  reagent. 

Reactions.  —  Put  a  trace  of  cystin  into  a  test-tube  with  some 
dilute  NaOH  and  a  little  lead  acetate.  Boil.  H2S  is  formed 
because  S  is  split  off. 

Tyrosin.  —  i.  Concentrate  the  neutralized  filtrate  of  6  of 
cystin  preparation  till,  on  cooling,  tyrosin  crystallizes  out. 

2.  Filter,  and  save  filtrate  for  the  preparation  of  leucin. 

3.  Dissolve  the  tyrosin  crystals  in  very  little  hot  water. 

4.  Add  amyl  alcohol  till  a  heavy  precipitate  forms. 

5.  Filter  precipitate. 

6.  Redissolve  in  very  little  hot  water,  and  let  crystallize  out 
by  cooHng. 

Examine  crystals  under  the  microscope. 
Test  with  Millon's  reagent. 

Leucin.  —  i .  Take  the  filtrate  of  2  in  the  preparation  of 
tyrosin,  and  evaporate  to  dryness  on  the  water  bath. 

2.  Extract  \vith  alcohol. 

3.  On  standing,  the  leucin  crystallizes  out  of  the  alcoholic 
extract  as  it  evaporates. 

4.  Filter,  and  dry  the  crystals. 
Examine  under  the  microscope. 

Gelatin.  —  Take  about  10  grams  of  bone,  preferably  small 
pieces  of  the  shaft  of  a  long  bone,  clean  carefully,  and  allow  to 
stand  for  a  few  days  in  60  c.c.  of  dilute  HCl  (1/20).  The  dilute 
acid  dissolves  the  inorganic  portion  of  the  bone,  leaving  the 
collagen.  Note  the  effervescence  due  to  the  presence  of  carbon- 
ates. The  acid  solution  is  poured  off  and  kept  for  further 
investigation.  The  remains  of  the  bone  are  allowed  to  stand 
overnight  in  a  dilute  solution  (i/io)  of  Na-jCOs,  and  then  boiled 
in  100  c.c.  of  water  for  an  hour  or  two.     The  collagen  undergoes 


PREPARATIONS  433 

hydrolysis  and  is  converted  into  gelatin,  which  dissolves.  A  core 
of  bone  untouched  by  the  acid  usually  remains.  Evaporate  the 
solution  to  25  c.c.  bulk  and  allow  to  cool.  A  firm  jelly  is  formed 
if  the  solution  is  sufficiently  concentrated.  If  the  solution 
gelatinizes,  add  an  equal  bulk  of  water  and  heat  anew.  If  the 
solution  thus  obtained  is  sufficient  in  quantity  it  may  be  used 
for  experiments  208  and  209. 

Gelatin  may  also  be  prepared  from  tendons  which  consist 
almost  wholly  of  white  fibers.  Collagen  is  the  substance  of 
which  white  fibers  are  made  up. 

Glycogen  (CeHioOsln.  —  Use  a  liver  taken  from  an  animal 
just  killed,  or,  if  the  season  permits,  oysters  just  removed  from 
the  shell.  Cut  an  oyster,  as  rapidly  as  possible,  into  small 
pieces,  and  throw  it  into  four  times  its  weight  of  boiling  water, 
sHghtly  acidulated  with  acetic  acid.  After  boiling  the  first  por- 
tion for  a  short  time,  remove  the  pieces,  grind  in  a  mortar  with 
some  sand,  return  to  the  water,  and  continue  the  boiling  for  sev- 
eral minutes.  FUter  while  hot.  The  opalescent  solution  thus 
obtained  is  an  aqueous  solution  of  glycogen  and  other  substances. 

If  a  purer  solution  is  desired,  continue  as  follows :  Add  to  the 
filtrate  alternately  a  few  drops  of  hydrochloric  acid  and  potassio- 
mercuric  iodide,  until  a  precipitate  of  protein  ceases  to  form. 
This  may  be  determined  more  conveniently  by  filtering  off  a 
small  portion  of  the  liquid  from  time  to  time,  and  adding  to- the 
clear  filtrate  the  hydrochloric  acid  and  potassiomercuric  iodide. 
WTien  the  precipitation  of  the  proteins  is  complete,  filter,  and  to 
the  milky  filtrate  add  double  its  volume  of  alcohol;  the  glycogen 
will  precipitate  as  a  white  powder.  Filter  this  off,  wash  with 
sixty-six  per  cent,  alcohol  (one  part  of  water  to  two  of  alcohol), 
and  dissolve  in  water. 

Mucin  Solution.  —  Cut  a  portion  of  a  navel-cord  into  small 
pieces.  Shake  in  a  flask  with  water,  changing  the  water  several 
times.  This  removes  salts  and  albumin.  Extract  for  twenty- 
four  hours  with  lime-water  or  baryta-water  in  a  corked  flask. 


434  APPENDIX 

Filter.  To  filtrate  add  acetic  acid,  which  precipitates  the  mucin. 
Let  settle,  filter,  and  wash  with  water. 

Mucin  may  also  be  prepared  from  the  saHva  by  precipitation 
with  acetic  acid. 

Potassium  Cyanate  (KCNO).  —  Melt  in  an  iron  ladle,  of  at 
least  50  c.c.  capacity,  five  grams  of  commercial  potassium  cyanide, 
and  stir  in  gradually  twenty  grams  of  litharge.  When  the  entire 
amount  has  been  added,  pour  the  mass  out  upon  an  iron  plate, 
and  allow  to  cool.  Separate  as  far  as  possible  the  reduced  lead 
from  the  potassium  cyanate  that  has  been  formed,  powder  the 
latter,  and  dissolve  in  25  c.c.  of  cold  water.  Filter  if  necessary 
and  purify  by  repeated  crystallization. 

Tyrosin.  —  See  paragraph  under  Cystin,  page  432. 

Urea,  Synthesis  of.  —  Add  to  a  filtered  solution  of  KCNO 
a  cold  saturated  solution  of  ammonium  sulphate,  containing 
at  least  six  grams  of  (NH)2S04.  Heat  the  mixture  slowly  on  a 
water  bath  at  a  temperature  of  60°  C,  and  maintain  at  that 
point  for  one  hour.  By  this  process  ammonium  cyanate  is 
formed  and  then  changed  to  urea,  which  may  be  obtained  in  an 
impure  state  by  evaporating  the  solution  to  dryness  on  a  water 
bath,  and  extracting  the  residue  with  hot,  strong  alcohol.  The 
urea  will  crystallize  from  the  alcohol  as  it  cools. 

Vegetable  Globulin :  e.g.  Edestin.  Extract  about  one  ounce 
of  crushed  hemp  seed  with  water  containing  about  5%  sodium 
chloride.  This  extraction  should  take  from  one-half  hour  to  one 
hour  at  a  temperature  of  about  60°  C.  Filter  while  hot.  Upon 
cooling,  a  portion  of  the  globulin  (edestin)  will  probably  separate 
out.  Use  the  clear  separated  fluid  for  the  general  protein 
reactions  and  precipitates.  Boil  the  cloudy  portion  until  the 
precipitated  globulin  has  dissolved.  Then  set  aside  for  twenty- 
four  hours  that  the  edestin  may  crystallize  slowly,  when  hexag- 
onal plates  should  be  obtained.  Examine  by  the  microscope. 
(See  Plate  VII,  Fig.  i,  page  287.) 


INDEX 


A. 

Absolute  temperature,  13 
Acetaldehyde,  208 
Acetamide,  235 

preparation  (Exp.  123),  393 
Acetanilide,  preparation  of,  249 

test  for,  229 
Acetates,  100 
Acetic  acid,  217 

(N/io)  factor,  151 
test  for  (acetates),  100 
volumetric  determination  of,  i^ 

anhydride,  218 

ether,  215 
Acetone,  210 

bodies,  224 

chloroform,  176 

exp.  with,  387 

in  blood,  210 

in  saUva,  300 

determination  of,  313 

in  urine,  350 

Legal's  test  for,  350 

preparation  of  (Exp.  90),  387 
Acetylene,  202 

preparation  of  (Exp.  67),  382 
Acetyl  chloride,  218 

salicylic  acid,  250  , 

urea,  239 
Achroodextrin,  263 
Acid  (defined),  4 

albumin,  276 

albuminate,  276 

ammonium  urate,  355 

groups,  93 

lactates  in  urine,  355 

metaprotein,  284 

preparation  of  (Exp.  224),  410 

phosphates  in  urine,  355 

potassium  oxalate,  221 

protein,  275 

salts,  4  - 

urates  (ammonium  and  sodium), 
Acidimetry,  149 
Acids  of  group  I,  tests  for,  93 

of  group  II,  tests  for,  95 

of  group  III,  tests  for,  98 

of  group  IV,  tests  for,  100 


Acids,  reactions  of,  91 
Acoin,  173 
Acrylic  acid,  219 

series,  219 
Acrylic  aldehyde,  219 
Activators,  258 
Addition  products,  199 
Adenin,  241 

Adjacent  hydrocarbons,  245 
Adnephrine,  174 
Adrenalin,  174 
I  chloride,  174 

Adrenol,  174 
Aich's  metal,  114 
Alabaster,  71 
Albumin  in  saliva,  298 

test  for  (Heller's),  314 

in  urine,  detection  of,  343 
Esbach's  test,  345 
heat  test,  344 
nitric  acid  test,  344 
Albvuninoids,  273,  277 
Albuminoscope,  344     - 
Albumins,  272,  275 

tests  for,  407 
Albumose  (Exp.  225),  411 
Albumoses,  285 
Alcohol,  206 

amyl,  207 

butyl,  207 

ethyl,  207 

grain,  207 

methyl,  207 

propyl,  207 

separation  of  water  from  (Exp.  76), 

384 
Alcoholates,  205 

Alcoholic  fermentation  in  milk,  284 
Alcohols,  205 

atomicity  of,  206 

classification  of,  206 

exp.  with,  384   . 
355  oxidation  of,  208 

Aldehyde,  208 

acetic,  208 

acrylic,  219 

benzoic,  250 

formic,  179,  208 

435 


436 


INDEX 


Aldehydes,  test  for  (Exp.  83,  84,  85), 

386 
Aldose,  259 

Algaroth,  powder  of,  39 
Aliphatic  hydrocarbons,  198 
Alkali  (defined),  4 

albumin,  276 

albuminate,  276 

aluminates,  57 

metaprotein,  285 

proteins,  275 
Alkalimetry,  149 
Alkaline  earths,  69 

exp.  with,  375 
Alkaline  metals,  78 

exp.  with,  376 
Alkyl  (term  defined),  note,  205 
Alkylated  ureas,  239 
Alloxan,  241 
Alloys  (defined),  114 

analj'sis  of,  166 

dental,  composition  of,  125 

eutectic,  117 

hst  of,  114,  115 

microscopical  examination  of,  117 

of  bismuth,  30 

of  cadmium,  31 

of  copper,  .26 

of  lead,  23 

of  mercury,  21 

of  silver,  19 

preparation  of,  115 
Allylene,  202 
Alum,  56 
Aluminates,  56 
Aluminium,  55 

alloys,  56 

amalgam,  121 

bronze,  56,  114 

cobalt  test  for.  59 

compounds,  56 

properties  of,  56 

reactions  of,  56 

solder  for,  130,  131 

sulphate,  56 
Alypin,  174 

andKI  (PI.  IV,  Fig.  6),  172 

microchemical  test,  174 

nitrate,  174 
Amalgam  (defined),  114 

alloy,  114 

effect  of  metals  in,  123 
Amalgamation  process  (silver  ore),  18 
Amalgams,  excess  of  mercury  in,  125, 
126 


Amalgams,  methods  of  making,  119 

properties  of,  119 

tests  for,  1 26 
Amandin,  273 

Ames,  Dr.,  on  use  of  beryllium,  140 
Ames'  oxyphosphate  of  copper,  138 
Amides,  235 
Amines,  233 
Amino  acetic  acid,  226 

acids,  225 

benzene,  248 

preparation  of  (Exp.  138),  396 

ethyl-sulphonic  acid,  232 

formic  acid,  225 
Amino  glutaric  acid,  227 

isobutyl-acctic  acid,  226 

phenol,  249 

succinic  acid,  227 

valeric  acid,  226 
Ammelid,  238 
Ammonia,  85 

alum,  56 

determination  in  urine,  335 

dilute,  424 

process  (NaaCOs),  82 

water,  85 
Ammoniacal  cuprous  chloride,  424 
Ammoniacal  silver  nitrate  solution,  334, 

425 
Ammoniated  mercury,  28 
Ammonium,  85 

acetate,  86 

acid  urate  (PI.  IX,  Fig.  i),  353 

amalgam,  121 

bifluoride,  174 

carbamate,  226 

carbonate,  85 
solution  of,  424 

chloride,  86 

(PI.  VIII,  Fig.  i),  316 
solution  of,  424 

compounds  of,  85 

cyanate  (Exp.  126),  393 

hydroxide  of,  85 

magnesium  phosphate,  75 

magnesium    phosphate   (microchemi- 
cal formation),  171 

molybdate  solution,  424 

nitrate,  86 

oxalate  solution  of,  425 

phosphate,  87 

picrate  (Exp.  148),  397 

platinic  chloride,  46,  47 
(PI.  Ill,  Fig.  i),  171 

reactions  of,  87 


INDEX 


437 


Ammonium,  salts,  86,  87 
in  saliva,  301 
determination  of,  310 

sodium  phosphate,  87 

sulphate,  86 

sublimed  (PI.  I,  Fig.  4),  106 

sulphide,  86 
solution,  425 
Amoss,  Dr.  H.  L.,  phenolphthalein,  Ref., 

300 
Amphoteric  reaction  of  milk,  281 
Amyl  acetate,  215 

alcohol,  207 

butyrate,  215 

nitrite,  215 

valeriate,  219 
Amylolytic  enzymes  in  saliva,  313 
Amylopsin,  321 
Anabolism  (defined),  361 
An£estheaine,  175 
Analytical  groups,  1 7 
Analysis  bj^  precipitation,  158 

in  dr}^  way,  102 

of  groups  {see  Groups) 

of  saliva,  304 
Anesthol,  175 
Aniline,  248 

oil,  248 

preparation  of  (Exp.  138),  396 
Annealing  of  alloys,- 116 

gold,  43 

platinum,  117 
Antialbumid,  276 
Antialbuminate,  276 
Antialbumose,  276 
Antifebrin,  preparation  of,  249 

test  for,  229 
Antimonite,  38 
Antimony,  38 

alloys,  39 

butter  of,  39 

in  dental  alloys,  124 

oxychloride,  39 

potassium  tartrate,  225 

properties  of,  38 

reactions  of,  39 

stains,  test  for,  36 
Antimonyl  salts,  39 
Antiseptic  tablets,  28 
Apatite,  72 
Apple  essence,  "219 
Aqua  ammonia,  85 

regia,  48 
Arabinose,  259 
Argentum,  18 


Argols,  80 
Argyrol,  175 
Arington's  alloy,  125 
Aristol,  175 
Aromatic  acids,  249 

hydrocarbons,  244 
experiments,  395 
Arrowroot  (PI.  VI,  Fig.  6),  262 
Arsenic,  antidote  for,  33 

compounds,  38 

in  urine,  determination  of,  352 

reactions  for,  33 

special  tests  for,  34  to  38  inc. 

stains,  tests  for,  36 

trioxide,  32 

(PI.  I,  Fig.  2),  106 

volumetric  determination,  157 
Arsenical  pyrites,  32 
Arsenious  acid,  32 

compounds,  32 

hydride,  33 
Arseno  benzol,  249 
Artificial  enamel,  138 
Ascher's  artificial  enamel,  139 
Asbestos,  74 
Ash  in  saliva,  315 
Asparaginic  acid,  227 
Asparagus,  succinic  acid  in,  221 
Aspartic  acid,  227 
Aspirin,  250 

Asymmetric  carbon,  223 
Atomicity  (defined),  4 

of  alcohols,  206 
Atoms  (defined),  2 
Atropin  and  test,  175 
Aurum,  42 

Available  oxygen  in  H2O2,  155  - 
Avogadro's  law,  14 

B. 

Babbitt's  metal,  128 

potash,  81 
Balanced  diet,  362 
Banca  tin,  40 
Barfoed's  reagent,  425 

solution,  261 

test  (Exp.  171),  401 
Barium,  70 

chloride,  solution  of,  425 

hydroxide,  70 

peroxide,  70,  180 

reactions  of,  70 

salts,  flame  test,  71 

sulphate,  70 
Baryta- water,  70 


438 


INDEX 


Base  (defined),  4 

metal,  16 
Basic  acetate  of  lead,  23 

salts,  5 
Basicity  of  acids,  216 
Bastard  metals,  16 
Battery  (cut),  113 
Bauxite,  55 
Bayberry  wax,  219 
Bead  test  with  microcosmic  salt,  109 
Bell-metal,  114 
Benedict's  solution,  425 

test  for  sugar,  348 
also  (Exp.  170),  401 
Benzaldehyde,  250 
Benzene,  244 

preparation  of  (Exp.  135),  395 
Benzidine,  248 

solution,  426 

test  for  blood  (Exp.  238),  414 
Benzine,  200 
Benzoated  lard,  250 
Benzoates,  250 
Benzoic  acid,  249 

experiments  with,  397 

sublimed  (PL  V,  Fig.  5),  204 
Benzol,  244 

Benzosulphinidum,  184 
Benzoyl  glycocoU,  251 
Beryl,  139 
Beryllium,  69 

test  for  in  cement,  139 
Berzelius'  test  for  arsenic,  36 
Beta  eucaine,  178 

and  PtCU  (PI.  Ill,  Fig.  2),  171 
Beta  oxybutyric  acid,  224 

in  urine,  351 
Bile,  322 

experiments  with,  422 

pigments,  tests  for  (Exp.  270),  422 

salts,    preparation    of    (Exp.    269), 
422 
Bilirubin,  322 
Biliverdin,  322 
Binary  amalgams,  121 
Biogen,  180 
Bismuth,  30 

alloys,  30 

compounds,  30 

in  dental  alloys,  124 

ochre,  30 

oxysalts  of,  30 

properties  of,  30 

reactions  of,  31 

sodium  stannite  test  for,  48 


Biuret,  238 

formation  of  (Exp.  127),  394 

reaction  (Exp.  189),  406 
Black  and  Sanger,  Gutzerits'  test,  37 
Black  ash,  82 
Black,  Dr.,  annealing  of  alloys,  116 

gold  in  alloys,  1 24 
Black's  dynamometer,  Ref.,  120 
Black  wash,  22 
Blast  furnace,  action  of,  53 
Blaud's  pills,  54 
Block  tin,  40 
Blood,  286 

benzidene  test  for,  414 

chicken  (PL  VII,  Fig.  6),  287 

corpuscles,  287 
number  of,  288 

dog  (PL  VII,  Fig.  5),  287 

experiments  with,  412 

fish  (PL  VII,  Fig.  6),  287 

frog  (PL  VII   Fig.  6),  287 

guaiacum  test  for,  413 

horse  (PL  VII,  Fig.  5),  287 

human  (PL  VII,  Fig.  5),  287 

plasma,  286 

serum,  286 

specific  gravity  of  (Exp.  236),  413 

spectroscopical  examination  of,  412 

urinary  sediment.  357 
Bloor's  nephelometer,  296 
Blow  pipe  tests,  107,  108 
Blue  stone  and  blue  vitriol,  27 
Boas'  reagent  and  test  for  HCl  (Exp. 

25Sc^  419 
Bond  (explained),  3 
Bone,  279 

earth,  279 

marrow,  279 
Borates,  99 
Borax,  176 

bead,  method  of  making,  61 

bead  test,  109 
Boric  acid,  tests  for,  99 
Brass,  114 

solder  for,  131 
Brick  dust  deposit,  241 
Britannia  metal,  114 
Bromoform,  203 
Bromides,  95 

separation  from  iodides,  97 
Bronze,  114 
Buckley,   Dr.  J.  P.,  Europhen,   Ref., 

179 
Buckley's  phenol  compound,  184 
Butane,  197,  201 


INDEX 


439 


Butter  ctystals  (PI.  VII,  Fig.  3),  287 

fat,  215 

of  antimony,  39 
Butylene,  202 

diamine,  234 
Butyric  acid,  218 
Butyrin,  215 
Bynin,  277 


Cacodyl,  204 
Cadaverin,  234 
Cadmium,  31 

alloys  of,  31 

amalgam,  123 

in  dental  alloys,  124 

oxalate  (microchemical),  171 

oxalate  (PL  II,  Fig.  2),  170 

reactions  of,  32 
Caffein,  241 
Calamine,  64 
Calcium,  71 

acid  lactate  (PL  VIII,  Fig.  4),  316 

in  saliva,  312 

in  teeth  and  tartar,  192 

lactate,  224 

(PL  VIII,  Fig.  3),  316 

metabolism  of,  364 

oxalate  (microchemical),  171 
(PL  II,  Fig.  i),  170 
in  urine,  356 

phosphate  in  tartar,  191 

reactions  of,  73 

sarcolactate,  224 

volumetric  determination  of,  162 
Calc-spar,  71 
Calomel,  21 
Calorie  (defined),  362 
Calverite,  42 
Camphors,  265 
Cane  sugar,  262 
Carat  (defined),  43 

rules  for  changing,  44 
Carbamic  acid,  225 
Carbamide  (Urea),  237 
Carbimide,  230 
Carbinol,  206 

Carbocyclic  compounds,  254 
Carbohydrates,  194 

classification,  ^59 

metabolism  of,  363 

Molisch's  test  for,  400 
Carbolic  acid,  176,  183 
Carbonates,  93 

in  saliva,  300 


Carbonates,  titration  of,  152 
Carbon  dioxide  in  saliva,  293,  296 

experiments,  380 
Carbonic  acid,  220 

in  teeth  and  tartar,  192 
Carbon    monoxide    hemoglobin    (Exp. 

23sd),  288 
Carbon,  test  for  in  organic  compounds, 
194 

tetrachloride,  203 
Carboxyl,  216 
Carbylamine,  233 
Carnallite,  78 
Carnin,  289 
"C.  A.  S."  alloy,  125 
Casein,  283 
Caseinogen,  283 
Cassiterite,  40 
Cast  iron,  53 
Casts,  fibrinous,  357 

renal,  357 
Catabolism  (defined),  361 
Catalase  (defined),  258 
Caustic  soda,  81 
Cellulose,  264 
Cement,  composition  of,  189 

dental,  135 

general  tests  for,  135,  136 
Centigrade  thermometer,  12 

to  Fahrenheit  degrees,  conversion  of, 

Centinormal  solution,  146 

Cerussite,  22 

Chalcocite,  26 

Chalcopyrite,  26 

Chalk,  71 

Charles,  law  of,  13 

Chase's  copper  amalgam  alloy,  125 

incisor  alloy.  125 
Chemical  affinity,  2 

equilibriiun,  8 
Chemism,  2 
Chih  saltpeter,  81,  83 
Chloral,  208 

alcoholate,  176 

hydrate,  176,  209 

test  for,  176  and  (Exp.  87,  88),  387 
Chlorates,  100 
Chlorethyl,  204 
Chloretone,  176 
Chlorides,  determination  of  in  saliva,  311 

in  urine,  336 

metabolism  of,  364 

tests  for,  94,  96 
Chlorinated  lime,  determination  of,  156 


440 


INDEX 


Chlorine  in  saliva,  titration  of,  i6o 

in  teeth  and  tartar,  192 

in  urine,  titration,  161,  337 

titration,  159 
Chloro-chromic  anhydride,  58 

test,  96 
Chloroform,  176,  203 

preparation  of  (Exp.  70),  383 

test  lor,  177 
Cholesterol,  323 

(Exp.  271),  423 

(PI.  VII,  Fig.  4),  287 

in  saliva,  301 
Chromates,  98,  99 
Chrome  alum,  56,  57 

iron  ore,  57 

yellow,  23 
Chromic  anhydride,  57 

o.xide,  57 

salts,  57 
Chromite,  57 
Chromium,  57 

compounds,  57 

reactions  of,  57 
Chromous  salts,  note,  57 
Chylous  urine,  328 
Chymosin,  322 
Cinnabar,  20 
Citric  acid,  222 
Classification  of  metals,  15 
Closed  chain  hydrocarbons,  244 
Closed  tube  test,  105 
Cloudy  urine,  causes  of,  328 
Coagulated  proteins,  275 
Coarse  solder,  129 
Cobalt,  61 

borax  bead,  61 

nitrite,  61 

reactions  of,  61 

separation  from  nickel,  67 

test  for  aluminium,  59 
Cobaltite,  61 
Cocaine,  177 

and  KMn04  (microchemical  crystals), 

(PL  III,  Fig.  4),  171 

and  substitutes,  differentiation  of,  188 

test  for,  177 

with  tin  chloride  (PI.  IV,  Fig.  3),  172 
Coefficient  of  Haeser,  331 
Coefficients  of  expansion,  112 
Coin  silver,  19,  114 
CoUagen,  278 
Colloidal  solution,  9 
Colloids,  10 


Colorimeter  (cut),  295 

Coloring  matter  in  urine,  341 

Color  reactions  for  proteins,  405 

Colors  of  salts,  103 

Color  test  for  amalgams,  126 

Colostrum,  284 

Common  solder,  129 

Completed  reactions,  5 

Complex  ions  (Exp.  122),  392 

Compound  ethers,  211,  214 

Compounds  (defined),  3 

Conductivity  of  metals,  in 

Condy's  fluid,  63 

Congo-red  solution,  426 

Conjugated  proteins,  274,  280 

Contraction  test  for  amalgams,  126 

Cook,  Dr.  G.  W.,  on  mucin  in  saliva, 

Ref.,  298 
Cook,  Dr.  R.  H.,  on  determination  of 

uric  acid,  Ref.,  334 
Cooking  soda,  79 
Copper,  26 

alloys,  26 

amalgam,  122 

black  oxide  of,  27 

compounds  of,  26 

glance,  26 

gravimetric  determination  of,  164 

in  dental  alloy,  124 

oxyphosphate  (Ames'),  138 

properties  of,  26 

pyrites,  26 

reactions  of,  27 

sulphate,  27 

for  Biuret  test,  426 

red  oxide  of,  26 

volumetric  determination  of,  161 
Copperas,  54 
Cork  in  urine  sediment  (PI.  IX,  Fig.  6), 

353 
Corn  starch  (PI.  VI,  Fig.  5),  262 
Corrosive  sublimate,  28,  181 
Corrugated  gold,  43 
Corundum,  55 

Cotton  fibers  (PI.  IX,  Fig.  6),  353 
Cotton  seed  oil,  219 
Cream  of  tartar,  80,  225 
Creatin,  289,  430 
Creatinin,  289,  431 
Creolin,  248 
Creosote,  177 

difference  from  carbolic  acid,  177 
Cresol,  177,  248 
Cresylic  acid,  248 
Crushing  strength  of  amalgams,  127 


INDEX 


441 


Cryolite,  81 

process  (NaaCOa),  82 
Cryoscopj',  14 
Crystalliziition,  experiments,  368 

Crystals,  formation  of,  169 

from  saliva,  3i() 
Cuprammonium  compounds,  27 
Cupric  oxide,  27 
Cuprous  oxide,  26 
Curd,  282 
Cyanamide,  235 
Cyanic  acid,  230 

(iso),  230 
Cj'anides,  test  for,  94 
Cyanogen,  228 
Cj^anogen  compounds,  228 

experiments,  391 
Cyanuric  acid,  238 
Cyclic  compounds,  254 
Cylinder  oil,  200 
Cystin,  227 

(Pl.X,  Fig.  6),355 

in  urine,  356 

preparation  of,  431 
Cystoglobulin,  274 

D. 

Dead  burnt  plaster,  72 
Decinormal  factor,  145 

solutions  (defined),'  146 
Defibrinated  blood,  286 
Degree  of  acidity  explained,  282 
Dental  alloys,  composition  of,  125 

cement,  135 

gold,  114 
Dentine,  composition  of,  189 
Derived  albumins,  276 

proteins,  274,  284 
Deutero  albumose  (Exp.  224),  411 
Dextrin.  263 
Dextrose,  260 
Diabetic  sugar,  260 
Diacetic  acid,  224 

in  urine,  351 
Dialyzer,  316 
Dial3'sis,  10 

(exp.  11),  369 

of  saliva,  316 
Diamines,  234 
Diastase,  262     ^ 
Dibasic  acids,  220 
Dichlor-methane,  203 
Diet,  "balanced,"  362 
Dilute  ammonia,  424 

hydrochloric  acid,  427 


Dilute  nitric  acid,  429 

sulphuric  acid,  430 
Dimcthylamine,  234 
Dimethyl-amino-azo-benzene    test    for 
HC'l  (Exp.  25s),  419 

solution  of,  426 
Dimethyl  arsine,  204 

benzene,  245 

ketone,  210 

oxalate  (Exp.  no),  390 
Diphenylamine,  249 
Dioses,  262 
Disaccharides,  262 
Diureides,  239 
Dolomite,  74 
Donovan's  solution,  t,^ 
Doremus-Hinds  urea  apparatus,  333 
Double-bonded  hydrocarbons,  201 
Dualistic  formulae,  3 
Ductility  of  metals,  in 
Dutch  metal,  115 

Du  Trey's  sjTithetic  porcelain,  Ref.,  140 
Dj'ad-mercury,  compounds  of,  28 

reaction,  29 
DjTiamometer,  Black's,  120 
Dysalbumose  (Exp.  224),  411 


Earthy  phosphates  in  urine,  337 
Edestin,  273 

preparation  of,  434 

(PL  VII,  Fig.  i),  287 
Egg  albumin,  275,  276 
Ektogan,  177 
Elastin,  278 
Electrons  (defined),  2 
Electro-properties  of  metals,  113 
Elements  (defined),  3 
Eleopten,  265 
Empirical  formulae,  3 
Emulsification  (Exp.  185),  404 
Enamel,  artificial,  138 
Enamel,  composition  of,  189 
Endelman,    Dr.,    on    phenolphthalein, 

Ref.,  183 
End  point  (defined),  145 
Enterokinase,  321 
EnzyTnes,  256 

experiments  with,  398 

properties  and  classification,  257 
Epinephrine,  177 
Epithelium  in  urine,  356 
Epsom  salt,  74 

Equations,  method  of  balancing,  6 
Equilibrium  (defined),  7,  9 


442 


INDEX 


Equivalent  weights  and  measures,  12 

Erepase,  323 

Erepsin,  323 

Erythrodextrin,  263 

Esbach's  reagent,  note  345,  426 

Essence  of  checkerberry,  250 

Esters,  211,  214 

exp.  with,  388 
Ethane,  200,  201 
Ether,  preparation  of,  212,  213 

(also  Exp.  93),  388 
Ethers,  211 
Ethyl  acetate,  214 

alcohol,  207 
Ethylates,  205 
Ethyl  benzene,  246 

bromide,  204 

butyrate,  215 

chloride,  178,  204 
Ethylene,  202 

-diamine,  234 

preparation  of  (Exp.  64),  382 
Ethyl  ether,  212 

hydrazine,  236 
Ethylidene  lactic  acid,  222 
Ethyl  mercaptan,  231 

nitrite,  214 

oxide,  212 

urea,  239 
Eucaine,  178 

and  PtCU  (PI.  Ill,  Fig.  2),  171 

lactate,  178 
Eudrenin,  178 
Eugenol,  179 
Europhen,  179 
Eutectic  alloys,  117 
Euzone,  180 

Evaporation,  microchemical,  170 
Expansion  of  metals,  112 

test  for  amalgams,  1 26 
Extraction  of  metals  from  ore,  15 

F. 
False  casts  and  mucin  (PI.  IX,  Fig.  5), 

353 
Fahrenheit  thermometer,  12 

to  Centigrade  degrees,  conversion  of, 

13 
Fat  acid  (PI.  VII,  Fig.  4),  287 

crystals  (PI.  VII,  Fig.  3),  287 

in  urine,  358 

of  milk,  284 
Fats,  215,  265 

chemistry  of,  265 

experiments  with,  403 


Fats,  metabolism  of,  363 

saponification  of,  267 
Fatty  acids,  216 

preparation  of  (Exp.  183),  404 
Fatty  casts,  358 
Fehling's  solution  426 
Fehling's  test  for  sugar  (Exp.  167),  401 
Fellowship  alloy,  125 
Fenwick,  Dr.  S.,  on  KCNS  in  saliva, 

Ref.,  302 
Ferments,  256 
Fermentation  test  for  sugar  (Exp.  172), 

349,  401 
Ferric  alum,  56 

chloride,  54 
solution  of,  426 

ferrocyanide,  55 

sulphate,  54 

sulphocyanate,  55 

ionization  of  (Exp.  16),  371 

thiocyanate,  55 
Ferricyanide,  detection  of,  97 
Ferris,   Dr.   H.   C,  methods  of  saliva 

analysis,  Ref.,  304 
Ferris  ureometer,  308 
Ferrous  carbonate,  54 

sulphate,  54 
Fibrin,  286 

ferment,  286 
Fibrinogen,  286,  and  (Exp.  241),  414 
Fibrinous  casts,  357 
Filtration,  microchemical,  170 
Fine  solder,  1 29 
Fire  damp,  200 
Flagg's  submarine  alloy,  125 
Flame  test,  106,  (note),  80 
Fleitmann's  test,  35 
Fletcher's  gold  alloy,  125 
Fletcher's  metallic  cement,  30 
Fletcher  melting  apparatus,  116 
Flow  of  amalgam,  120 
Folin's  ammonia  test,  310 

new  method  for  ammonia  in  urine,  335 
Fool's  gold,  53 
Formaldehyde,  208 

method  for  ammonia  in  urine,  336 
Formaldehydurea,  354 

(PI.  X,  Fig.  5),  355 
Forma;lin,  1 79 

test  for,  385,386 
Formamide,  235 
Formanilide,  235 
Formic  acid,  217 

ether,  212 
Formine,  179 


INDEX 


443 


Formol,  179 

Formose,  208 

Formula  (defined),  3 

Fowler's  solution,  33 

Fractional  distillation,  200 

French  chalk,  74 

Freund  &  Topfer,   test  for  acidity  of 

urine,  330 
Frohde's  reagent,  182 
Fruit  sugar,  261 
Fulminic  acid,  230 
Furfuraldehyde,  260 
Fusel  oil,  207 
Fusible  metals,  128 


Gad's  experiment  (Exp.  185),  404 

Galactose,  261 

Galena,  22 

Gallic  acid,  251 

Gallotannic  acid,  186 

Garnierite,  62 

Gasolene,  200 

Gastric  contents,  analysis  of,  417 

titration  for  acidity  (Exp.  260),  421 
Gastric  digestion,  319 

lipase,  320 
Gay-Lussac,  law  of,  13 
Gelatine,  279 

experiment  with,  409 

preparation  of,  432  ' 
German  silver,  62,  115 
Glacial  acetic  acid,  217 
Glauber's  salt,  84   . 
GKadin,  277 
Globin,  273 
Globulins,  272,  276 

reactions  of,  277 

tests  for,  407,  408 

vegetable,  434 
Glonoin,  spirit  of,  182 
Gluciniun,  69 
Gluconic  acid,  260 
Glucosazone,  261 

(Fig.  I,  PI.  VI),  262 
Glucose,  260 

tests  for,  261  (also  Exp.  167,  etc.) 
Glue,  279 
Glutamic  acid,  227 
Glutelins,  277 

(defined),  273  ^ 
Glutenin,  277 

Glycerol  (glycerine),  179,  215 
Glyceryl,  215 

butyrate,  215 


Glyceryl,  oleate,  266 

palmitate,  266 

stearate,  266 
Glycin,  226 

Glycocholic  acid  in  bile,  323 
GlycocoU,  226 

relation  to  urea,  323 
Glycogen,  263 

isolation  of,  433 

in  muscle,  290 

in  saliva,  312 
Glycol,  220 
Glycollic  acid,  222 
Glyco-proteins,  280 

(defined),  274 
Glyoxylic  acid  (Exp.  190),  406 
Gmelin's  test  for  bile  (Exp.  270),  422 
Gold,  42 

alloys,  43 

aluminium  solder,  131 

amalgam,  122 

annealing  of,  43 

carat,  43 

corrugated,  43 

gravimetric  determination  of,  165 

in  dental  alloys,  124 

melting-point  of,  42 

non-cohesive,  43 

precipitation  of,  45 

reactions  of,  44 

scraps,  recovery  of,  141 

solders,  131,  132,  133 

solubility  of,  42 

volumetric    determination    of,    157, 
158 
Goulard's  extract  (lead  subacetate),  23 

preparation  of,  426 
Grain  alcohol,  207 
Gram's  solution  (iodine),  179 

strength  of,  426 
Grape  sugar,  260 
Graphic  formulae,  3 

tellurium,  42 
Gravimetric  determination,  163-167 
Gravity,  specific,  13 
Green  vitriol,  54 
Group  I,  analysis  of,  24 
exp.  with,  372 
outline  of,  25 

II,  analysis  of,  47 
exp.  with,  372 
outline  of,  51 

III,  analysis  of,  58 
exp.  with,  373 
outline  of,  60 


444 


INDEX 


Group  IV,  analysis  of,  66 
exp.  with,  374 
outline  of,  68 

V,  analysis  of,  75 
exp.  with,  375 
outline  of,  77 

reagents,  16 
Groups  I- VI,  metals  of,  17 

III,  IV  and  V  analysis,  90 

phosphates  present,  88 
Guaiacol,  246 

Guaiacum  test  for  blood  (Exp.  237),  413 
Guanin,  241 
Gun  cotton,  264 
Gun  metal,  115 
Gunzburg's  reagent,  419,  426 

test  (Exp.  2S5b),  419 
Gutta-percha,  179 
Gutzeit's  test,  34 

Gutzeit's  test  (Sanger  and  Black),  37 
Gypsum,  71 

H. 

Halogens  (organic),  test  for,  196 
Haloid  derivatives  of  the  paraffins,  203 
Hard  solder,  129 
Harris'  amalgam  alloy,  125 
Head,    Dr.    Joseph,    bifluoride   of   am- 
monia, Ref.,  174 
Heavy  spar,  70 
Helium,  70 
Hematite,  brown,  53 
Hematite,  red,  53 
Hematin,  288 
Hematopophyrin,  328 
Hemin,  289 

crystals,  preparation  of  (Exp.  239) ,  4 14 
Hemialbumose,  276 
Hemipeptone,  276 
Hemochromogen,  287 
Hemoglobin,  288 

cr>'stals,  preparation  of  (Exp.  234), 41 2 
Hemoglobins  (defined),  274 
Heroin,  180 
Heteroalbumose,  411 
Heterocyclic  compounds,  254 
Heteroxanthin,  241 
Hexoses,  260 
High-grade  alloy,  125 
Hile,  Dr.  E.  O.,  on  Du  Trey's  porcelain, 

140 
Hippuric  acid,  226,  251 

(PI.  V,  Fig.  4),  204 
Histones  (defined),  273 
Hofmann's  carbylamine  reaction,  233 


HomocycHc  compounds,  254 
Homologues,  197 
Hopkins-Cole  reagent,  427 
reaction  (Exp.  190),  406 
Hopkin's  method  for  ammonia  in  urine, 

335 
Hopogan,  180 
Hordein,  277 
Horismascope,  344 
Horn  silver,  18 
Howe,  Dr.  J.  Morgan,  KCXS  in  saliva, 

Ref.,  303 
Howe,  Dr.  Percy  R.,  calcium  determi- 
nation, Ref.,  162,  312 
Howe,    Dr.    Percy    R.,    phosphates   in 

saliva,  87 
Howe,  Dr.   Percy  R.,  tartar  deposits, 

190 
Hydrargyrum,  20 
Hydrazines,  235 
Hydraulic  mining,  42 
Hydrocarbons,  ig6 

experiments  with,  380 
Hydrochloric   acid,  vol.   determination 
of,  151 

dilute,  427 

in  stomach,  320 

test  for  free  (Exp.  255),  419 
Hydrocyanic  acid,  228 

preparation  of  (Exp.  115),  391 
Hydrogen  dioxide  (peroxide),  180 

factor  for,  155 

preparation  of,  371 

strength  of,  155 

test  for  in  organic  compounds,  194 
Hydrolysis,  defined,  4,  8 

experiments,  370 
Hydroquinol,  247 
Hydroxy  acids,  222 

acetic  acid,  222 

benzene  (phenol),  183,  246 

propionic  acid,  222 

succinic  acid,  222 

toluene,  248 
Hypobromite  solution  for  urea,  427 
Hypochlorite  determination,  156 

test  for,  96 

reaction  with  silver  nitrate,  95 
H>'pophosphites,  test  for,  97 
H>T)0.xanthin,  241 


I. 


Ignition  tests,  104 
Imides,  234 
Imino  group,  234 


INDEX 


445 


Indicators,  148 

Indol,  253 

Indoxyl  (indican),  253 

in  urine,  341 

-potassium  sulphate,  253 
Inorganic  matter  in  teeth  and  tartar, 

191 
Inositc,  290 
Intestinal  juice,  323 
Invertase,  427 

Iodides,  separation  from  bromides,  97 
Iodine,  N/io  solution  of,  155 

determination,  156 

in  ductless  glands,  366 

(PI.  I,  Fig.  6),  106 

solution,  427 

test  for  bile  pigment  (Exp.  270),  423 

tincture  for  reagent,  427 
Iodoform,  204 

(PI.  V,  Fig.  i),  204 

preparation  of  (Exp.  72),  383 
Ionization,  7 

(Exp.  16),  371 

(Exp.  122),  392 
Ions,  3 
Iridium,  46 
Iron,  53 

by  hydrogen,  54 

compounds  of,  54 

melting-point  of,  54 

metabolism  of,  365' 

pyrites,  53 

reactions  of,  54  and  (Exp.  30,  31),  373 

reduction  from  ore,  53 
Iron  scale,  salts  of,  225 
Isobenzonitril,  229 

test  for  chloral,  387 
Isobutyl  carbinol,  207 
Isocyanic  acid,  230 
Isocyclic  compounds,  254 
Isomers,  197 
Isomerism,  197 

physical  {see  stereoisomerism) 
Isonitrils,  229 

K. 

Ealium,  78 

Kekule's  benzene  ring,  244 
Kephir  grain,  284 
Kerargyrite,  18 
Keratins,  278    ^ 

experiments  with,  408 
Kerosene,  200 , 
Ketones,  209 
Ketose,  259 


Kieserite,  74 

King's  occidental  alloy,  125 

Kingzett's      method      for      hydrogen 

peroxide  titration,  156 
Kirk,  Dr.  E.  C,  carbon  dioxide  in  blood, 

Ref.,  300 
Kjeldahl  process  of  oxidation,  195 
Kumiss,  284 

L. 

Lacmoid,  148,  247 
Lactalbumin,  283 
Lactic  acid,  222 

in  muscle,  290 

in  tartar,  191 

optical  activity  of,  223 

test  for  (E.xp.  114),  391 

test  for  (Exp.  257),  420 
Lactose,  262 

Lactosazone  (PL  6,  Fig.  3),  262 
Lard  crystals  (PL  VII,  Fig.  3),  287 
Law  of  Avogadro,  14 

Charles,  13 

Gay-Lussac,  13 

partition,  9 
Lead,  22 

acetate,  23 

alloys,  23 

arsenate,  23 

black  oxide  of,  23 

compounds  of,  23 

in  urine,  determination  of,  352 

oxides,  23 

properties  of,  22 

reactions  of,  23,  24 

reduction  from  lead  sulphide,  22 

solubilit}'  in  water,  22 

subacetate,  23 

solution  of,  428 
LeBlanc  process   (sodium   carbonate), 

82 
Lecithin,  267 

in  saliva,  301 
Lecitho-proteins  (defined),  274 
Legal's  test  for  acetone,  350 
Leptothrix,  318 
Leucin,  226 

_(PLV,Fig.  2),204 

in  saliva,  301 

preparation  of,  428 
Leucocj'tes,  288 
Le^allose,  210,  261 
Ligno-cellulose,  264 
Limestone,  71 
Limonite,  53 


446 


INDEX 


Lipase,  322 

from  castor  bean  (Exp.  159),  399 
preparation,  428 

from  pancreas,  428 
Litharge,  23 
Lithium,  84 

salts  and  uric  acid,  242 
Litmus,  148 
Liver  of  sulphur,  80 
Local  anesthetics.  173 
Low's  gold  solder.  133 
Lugol's  caustic  iodine,  181 

iodine  solution,  181,  428 
Lunar  caustic,  20 
Lycopodium  (PI.  IX,  Fig.  6),  353 

M. 
MacDoiiald,    Dr.    C.    F.,    oxidases    in 

saliva,  299 
Magnalium,  56 
Magnesia,  light  and  heavy,  74 

mixture,  428 
Magnesite,  74 
Magnesium,  74 

acid  lactate  (PI.  VIIL  Fig.  4),  316 

alloys,  74 

amalgam,  122 

ammonium  phosphate  (PI.  IV,  Fig.  2), 
172 

carbonate,  74 

compounds,  74 

effect  of,  on  metabolism,  365 

in  teeth  and  tartar,  192 

lactate  (PI.  VIII,  Fig.  3),  316 

o.xide,  74 

phosphates,  75 

reactions  of,  74 

sulphate,  74 

hydrate  titration  of,  152 
Mahe,    Dr.    G.,    sodium   chloride   and 

toxicity,  Ref.,  185 
Malachite  blue,  and  green,  26 
Malic  acid,  222 

test  for  in  vinegar  (Exp.  113),  391 
Malleability  of  metals,  iii 
Malonic  acid,  221 
Maltodextrin,  263 
Maltase.  298 
Maltose,  262 

Maltosazone  (PI.  VI,  Fig.  2),  262 
Manganates,  64 
Manganese,  63 

compounds,  63 

hydroxide,  64 

reactions,  63 


Manganese,  red  lead  test  for,  63 

separation  from  zinc,  67 
Mannheim  gold,  115 
Maimite,  206 
Marble,  71 

Marme's  reagent,  428 
Marsh-Berzelius  test  for  arsenic,  36 
Marsh  gas,  200 

preparation  of  (Exp.  63),  381 
Marsh's  test  for  arsenic  or  antimony,  35 
Mass  action,  8 

(defined),  i 
Mayer,  A.,  on  potassium  sulphocyanates 

in  saliva,  Ref.,  302 
McCaulev,   Dr.,   on   copp>er   in   alloys, 
Ref.,' 1 23 

on  zinc  in  alloys,  Ref.,  124 
McElhinney,      5lark      G.,      platinum 

solders,  Ref.,  133 
Measures,  11 
Meerschaum,  74 
Meconic  acid,  389,  417 
Mellot's  metal,  128 
Melting-point  of  metals,  in 

method  of  taking,  129 
INIenthol,  181 
Mercaptan,  231 
Mercaptol,  231 
Mercuric  bromide  test  for  arsenic,  37 

chloride,  28,  181 

reaction  with  SnCU,  29 

solution.  428 

subhmed  (PI.  I,  Fig.  3),  106 

iodide,  29 

oxide,  red,  28 

oxide,  yellow,  28 
Mercurous  chloride,  21 

iodide,  21 

nitrate,  21 

oxide,  black,  22 
Mercury,  20 

alloys  of,  21 

compounds  of,  2 1 

excess  of  in  amalgams,  125 

from  mercuric  oxide  (PI.  I,  Fig.  5),  106 

in  saliva,  test  for,  317 

properties  of ,  21 

reactions  of,  22,  29 

recover},- of,  142 

succinimide,  234 

tests  for  purity,  142 
Mesitylene,  246 
Metabolism,  361 
Meta-compounds  (defined),  245 
^leta-cresol,  248 


INDEX 


447 


Metallic  cement,  Fletcher's,  30 

Metalloids,  16 

Metals,  classification,  15,  16 

extraction  of,  15 

group  I,  etc.  {see  Group) 

occurrence  of ,  15 

properties  of ,  iii,  112 

melting-points  of,  11 1 
Metaphosphate  cement,  135 
Metaprotein,  2S4 

(defined),  274 

preparation  of,  410 
Metastannic  acid,  40 
Methane,  197,  200 
Methethyl,  181 
Methyl-alcohol,  206 

test  for,  385 

-amine,  234 

-benzene,  245 

bromide,  203 

carbamine,  229 

carbinol,  207 

chloride,  1S2,  203 

chloroform,  203 
IMethylene  chloride,  203  ' 

ether,  212 
Methyl  ether,  212 

eth}'!  ether,  212 

hydrazine,  235 

indol,  234 

iodide,  203 

orange,  148 

oxide,  212 

salicylate,  250 

urea,  239 
^Metric  equivalents,  12 
Michaels,  Dr.  J.  P.,  albumin  in  saliva, 

Ref.,  298 
Michaels,  Dr.  J.  P.,  methods  of  saliva 

analysis,  Ref.,  305 
Microchemical  analj'sis,  168 
Microchemical  methods,  169,  170 
Microscosmic  salt,  87 
Microscope,  use  of,  168 
Milk,  281 

alcoholic  fermentation,  284 

experiments  with.,  409 

fat,  284 

modified,  2 S3 

of  magnesia",  titration  of,  152 

plasma,  281 

reaction  of,  281,  282 

specific  gra\-ity  of,  281 

solids  by  calculation,  281 

wme,  2  84 


Miller,  Dr.  W.  D.,  mucin  in  saliva,  Ref., 

298 
Millon's  reagent,  preparation  of,  428 

test  (protein),  405 
Mineral  oil,  199 
Mineral  salts,  metabolism,  366 
Minium,  23 
Mixed  ether,  211 
Modified  milk,  283 
Mohr's    method    of    determination    of 

arsenic,  157 
Moisture  in  teeth  and  tartar,  191 
Molar  solution  (defined),  144 
Molecules  (defined),  2 
Molisch's  reagent,  429 
Molisch's  test  for  carbohydrates,  400 
Monobrom-methane,  203 
Monochlor-methane,  178 
Monosaccharides,  259 
Monoses,  260 
Monsel's  salt,  54 
Morphine,  182 

(PI.  Ill,  Fig.  6),  171 

(microchemical  test),  171,  172 

and  Marme's  reagent  (PI.  IV,  Fig.  i), 
172 
Mosaic  gold,  115 

Moth  scales  (PI.  IX,  Fig.  6),  353 
Mucic  acid,  298 
Mucin,  280 

experiments  with,  410 
,  (PI.  IX,  Fig.  5),  353 

from  navel  cord,  433 

in  saliva,  297 

in  urine,  358 
Mucoids,  274 
Murexide,  note,  242 

test,  uric  acid  (Exp.  131),  394 
Muscle,  2  89 

experiments  with,  415 

plasma,  289 

serum,  289 
Musculin,  415 
Myogen,  415 
Myogenfibrin,  415 
Myosin,  289 

(Exp.  243c),  415 
Myosinfibrin,  415 
Myosinogen,  289,  415 

N. 
Naphtha,  200 
Natrium,  81 
Nephelometer,  296 
Nessler's  reagent,  29,  429 


448 


INDEX 


Neutral  salts,  s 
Nickel,  62 

alloys,  62 

borax  bead,  63 

coin,  62 

plating,  62 

reactions  of,  63 

separation  from  cobalt,  67 
Nirvanin,  182 
Niter,  79 
Nitrates,  100 
Nitric  acid,  dilute,  429 
Nitrils,  229 
Nitrites,  detection  of,  97 

in  saliva,  303,  313 
Nitrobenzene,  248 

preparation  of  (Exp.  137),  395 
Nitrocellulose,  264 

Nitrogen,    tests    for    in    organic    com- 
pounds, 194 
Nitroglycerine,  182 
Nitrous  oxide,  preparation  of,  86 
Noble  metals,  15 
Non-cohesive  gold,  43 
Normal  factor  (defined),  144 
Normal  salt  solution  (physiological),  83 
Normal  solution  (defined),  143 
Novocaine,  183 
Nucleohistone,  274 
Nucleoproteins  (defined),  274 

O. 

Occurrence  of  metals,  15 
Odontographic  alloy,  125 
Oil  of  bitter  almonds,  250 

cloves,  183 

gaultheria,  test  for,  183 

mirbane,  248 

wintergreen,  250 
Oils,  265 

experiments  with,  403 
Olefin  series  of  hydrocarbons,  202 
Oleic  acid,  219,  266 
Optical  analysis,  sugar  solution,  349 
Organic  acids,  216 

chemistry,  193 

experiments  with,  389-390 

matter  in  teeth  and  tartar,  191 
Orpiment,  32 

Ortho-compounds  (defined),  245 
Orthocresol,  248 
Orthoform,  183 
Osazones,  261 
Osmosis,  10 

(Exp.),  369 


Osmotic  pressure,  10 

Outline  analysis,  group  I-V,  25,  51,  60, 

68,77 
Outline  analysis  of  groups  III-V,  phos- 
phates present,  90 
Ovoglobulin,  273 
Oxalates,  95,  99 

in  urine,  356 
Oxalic  acid,  220 

(sublimed)  (PI.  I,  Fig.  i),  106 

natural  sources  of,  221 

standard  solution  of,  149 

in  tartar,  iqo 

preparation  of,  221 
Oxaluric  acid,  239 
Oxidation  of  alcohols,  208 
Oxidases  {see  oxydases)  258 
Oxidation  and  reduction,  analysis  by, 

153 
Oxidation  (Exp,  i,  2,  3),  367 
Oxyacids,  222 
Oxybenzene,  246 
Oxybutyric  acid,  224 
Oxychloride  cements,  137 

of  zinc,  137 
Oxydase  in  saliva,  detection  of,  314 
Oxydases,  258 

preparation  of  (Exp.  155),  598 

in  saliva,  299 
Oxyhemoglobin,  288 
Oxyphosphate  cement,  137 

of  copper  cement,  138 
zinc,  135 
Oxypropionic  acid,  222 
Oxysulphate  of  zinc,  137 


Palmitin,  219 

note,  experiment,  181 
Palmitic  acid,  217,  219 

(Plate  IV,  Fig.  s),  172 
Pancreatic  digestion,  321 

extract,  429 

juice,  321 

(Exp.  261),  421 

rennin,  322 
Parabanic  acid,  239,  241 
Para  compounds  (defined),  245 
Para  eresol,  248 
Para-acet-phenetidine,  249 
Paraffin,  199 

oil,  200 


series,  197 

wax,  199 

Paraform,  208 


INDEX 


449 


Paraformaldehyde,  208 
Paraglobulin  (Exp.  202),  408 
Paralactic  acid,  223 
Paraldehyde,  208 
Paramyoiinogen,  289,  415 
Paris  green,  27 
Pearl  ash,  79 
Pearson's  solution,  33 
Pentane,  197 
Pentoses,  259 
Pepsin,  319 

hydrochloric  acid,  417 
Pepsinogen,  319 
Peptides,  275,  286 
Peptones,  275,  285 

experiment  with,  411 
Permanganate,  standardization  of,  153 
Peroxidases,  258 

in  saliva.  299 
Peroxide  of  calcium,  180 

hydrogen,  180 

preparation  of  (Exp.  17),  371 
strength  of,  154 
titration  by  KMn04,  154 
titration  by  Xa2S203,  155,  156 

lead  {see  black  oxide),  23 

sodium,  81,  180 

zinc,  180 
Petroleum  jelly,  200 
Pewter,  40 
Phase  (delined),  6 
Phenacetine,  249 
Phenol.  183.  246 

compound,  1S4 

diilerence  from  cresol,  177 

preparation  of  (Exp.  154),  398 

test  for.  184 
Phenolphthalein,  14S,  252 
Phenolphthalin.  299 
Phenol-sulphonic  acid,  252 

preparation  of,  429 
Phenyl-formamide,  235 

-glucosazone,  261 

-hydrazine,  236 

test  for  sugar,  (Exp.  173),  401 
solution,  429 

-isocyanide,  229 

-salicylate,  250 
Phenol-snilphonic  acid,  252 

-sulphuric  acid,  252 
Phenyl-hj'drazine  test,  349,  401 
Phloroglucinol,  247 
Phosphates,  95,  98,  99 

as  urinar>'  sediment,  338 

determination  in  saliva,  312 


Phosphates,  in  saliva,  300 

metabolism  of,  365 

in  urine,  355 

of  sodmm,  83 

titration  with  uranium,  339 
Phospho-proteins  (defined),  274 
Phosphoric  acid,  factor,  339 

in  teeth  and  tartar,  192 

ionization  of,  8 

titration  with  uranium  nitrate,  339 
Phosphorus,  test  for,  195 
Phthalic  acid,  252 

anhydride,  252 
Physical  isomerism,  224 
Physiological  chemistr>',  256 

salt  solution,  83 
Picric  acid,  249 

solution,  429 
Pig  iron,  53 
Pineapple  essence,  215 
Piotrowski's  test  (Exp.  189),  406 
Pitchblende,  70 
Placer  mining,  42 
Plaster  compoimd,  73 

expansion  of.  73 
Plaster  of  Paris,  72 

slabs,  preparation  of,  107 
Plate  I,  106 

II,  170 

III,  171 

IV,  172 

V,  204 

VI,  262 

VII,  287 

VIII,  316 

IX,  353 

X,  355 
Platinum,  45 

alloys.  46 

aluminium  solder,  131 

amalgam,  123 
^  annealing  of,  117 

black,  45 

color,  for  enamel,  46 

in  dental  alloy,  125 

reactions  of,  46 

solder  for,  133 
PohTners,  198 
Poly  OSes,  262 
Polysaccharides,  262 
Poly  sulphides,  80,  87 
Potash  alum.  56 
Potassio-auric  iodide,  45 
Potassio-mercuric  iodide,  29 
Potassium,  78 


45° 


INDEX 


Potassium,  antimony  tartrate,  225 

bicarbonate,  79 

bi tartrate,  80,  225 

bromate,  79 

bromide,  79 

carbonate,  79 

chlorate,  80 

chloride  (PI.  VIII,  Figs.  5,  6),  316 

compounds  of,  78 

cyanate,  230 

preparation  of,  434 

cj'anide,  79,  228 

hydrolysis  of,  229  (also  Exp.  119) 

ethylate,  205 

ferricyanide,  230 

ferrocyanide,  229 
solution,  429 

hydroxide,  78,  184 

iodide,  79 

iodo-hydrargyrate,  29 

methylate,  205 

nitrate,  79 

permanganate,  63 

phenolate,  246 

platinic  chloride,  47,  80 
(PI.  Ill,  Fig.  3),  171 

reactions  of,  80 

salts  of,  79,  80 

effect  on  metabolism,  364 

sulphide,  80 

sulphocyanate  (thiocyanate)  in  saliva, 
301 

standard  solution  of,  160 
test  for  (Exp.  247),  417 
Potato  spirit,  207 

starch  (PI.  VI,  Fig.  6),  262 
Precipitation,  11 
Primary  alcohol,  206 

amines,  233 

ionization,  8 
Prinz,  Dr.  H.,  on  phenol  sulphonic  acid, 

Ref.,  253 
Proenzymes  (defined),  257 
Prolamines,  277 

(defined),  273 
Propane,  197,  201 
Propenyl,  215 
Propionic  acid,  218 
Propylene,  202 
Prosecretin,  324 
Protamines  (defined),  273 
Proteans  (defined),  274 
Protein  (defined),  272 
Proteins,  269 

classification  of,  269 


Proteins,  color  reactions  of  (Exp.  187- 

190),  405 

metabolism  of,  363 

precipitants  of  (Exp.  191-195),  406 
Proteolytic  enzymes  in  saliva,  299 
Proteoses,  285 

experiment  with,  411 
Proteoses  (defined),  275 
Prothero,  Dr.  J.  H.,  Ref.,  72 
Proto-albumose,  411 
Proximate  analysis,  194 

principles,  194 
Prussian  blue,  55 
Prussic  acid,  228 
Pseudo-cellulose,  264 
Pseudo-nucleo-albumin,  283 
Ptomaines,  234 
Ptyalin  {see  also  amylolytic  enzymes) 

action  on  starch  (Exp.  245),  416 

conditions  affecting  action  of  in  saliva 
(Exp.  246),  298 
Purin,  240 

nucleus,  240 
Purple  of  Cassius,  45 
Pus  (defined),  288 

urinary  sediment,  357 

(PI.  IX,  Fig.  3),  353 
Putrescin,  234 
Pyknometer  (cut),  307 
Pyridin,  254 

Pyrocatechin  (pyrocatechol),  246 
Pyrogallic  acid,  247 
Pyrogallol,  247 
Pyrolusite,  63 
Pyrotartaric  acid,  221 

Q- 

Qualitative  analysis,  15 

of  dental  alloys,  166 
Quantivalence,  4 
Questions  on  group  I,  25 

group  II,  51 

group  III,  60 

group  IV,  68 

group  V,  77 

group  VI,  88 
Questions  on  volumetric  work,  167 
Quinalin,  254 

R. 

Racemic  compounds,  225 

Radium,  70 

Reaction  of  saliva,  292 

Reactions,  completed  and  reversible,  $ 

Realgar,  32 


INDEX 


451 


Red  blood  corpuscles,  287 
Red  lead,  23 

test  for  manganese,  63 
Red  precipitate,  29 
Red  prussiate  of  potassium,  230 
Reduced  iron,  54 
Recs's  alloy,  40 
Reinsch's  test  for  arsenic,  34 
Renal  casts,  357 

(PI.  IX,  Fig.  4),  353 

epithelium,  356 
Rennin,  320 

(Exp.  253),  419 
Residue,  recovery  of  gold,  141 

mercur>-,  142 

silver,  141 
Resorcinol,  247 
Reticulin,  278 
Reversible  reactions,  5 
Rliigoline.  184,  200 
Rice  starch  (PI.  VI,  Fig.  V),  262 
Richmond,  Dr.   C.  M.,  fusible  alloy, 
128 

gold  solder,  133 
Ringer's  solution,  184 
Rochelle  salts,  84,  225 
Rock  oil,  199 
Rose's  metal,  128 
Rose's  reaction,  370 
Rule  for  changing  ■  C.   to  F.  degrees, 
13 


Saccharic  acid,  260 
Saccharin,  184 
Saccharin,  test  for,  184 
Saccharose,  262 
Salammoniac,  86 
Saleratus,  79,  82 
Salicylates,  250 
Salicylic  acid,  250 

test  for  (Exp.  153),  398 
Saliva,  291 

acetone  in,  313 

acidity  of,  293 

action  on  starch  (Exp.  245),  416 

albumin  in,  314 

alkalinity  of,  292,  319 

ammonium  salts  in,  301 

analysis  blank  and  use,  360 

anah'sis  of,  304 

carbon  dioxide  in,  293 

color  of,  296 

constituents  of,  297 

determination  of  ammonia,  310 


Saliva,  determination  of  ash,  315 
of  chlorides,  311 
of  nitrites,  313 
of  phosphates,  312 
of  potassium  sidpho-cyanate,  308 
of  soUds,  315 
of  specific  gra\'ity,  308 

determination  of  lurea,  311 

dialyzed,  316 

enzjTnes  in,  313,  314 

experiments  with,  416 

glycogen  in,  312 

lactic  acid  in,  317 

mucin  in,  297,  314 

nitrates  in,  303 

nitrites  in,  303 

odor  of,  297 

ox}-dase,  detection  of,  314 

physical  properties  of,  292,  305 

ptyalin  in,  298 

quantity  of,  292 

reaction,  292,  307 

specific  gra\-ity,  292 

sulphocyanates  in,  302 

variation  in  composition,  291 

viscosity  of,  305 
Salivar\-  sediment,  318 
Salmine,  274 
Salol,  250 
Sal  soda.  81 
Salt  (defined),  4 
Salt  of  sorrel,  221 
Saltpeter,  79 
Salts  in  metabolism,  364 
Salts  of  tartar,  79 
Salt  solution,  decLnormal,  159 
Salvarsan,  249 

Sanger  &  Black  (Gutzeit's  test),  Ref.,  37 
Saponification  (Exp.  182),  403 
Sarcolactic  acid,  223 
Saturated  hydrocarbons,  199 
Scale  salts  of  iron,  225 
Schiff's  reagent,  429 
Scombrone,  273 
Secondar}^  alcohol,  206 

amines,  234 
Secondary'  protein  derivatives,  275 
Secretin,  323 
Sediment  in  saliva,  318 
Sediment  in  urine,  353 
Semipermeable  membrane,  10 
Serimi  albumin,  286,  275,  276 

blood,  286 

globulin,  286 
Sidenite,  53 


452 


INDEX 


Silver,  i8 
alloys,  19 

alloy,  60  per  cent,  125 
amalgam,  123 
decinormal  solution  of,  159 
fire  assay,  165 
glance.  18 

gravimetric  determination  of,  164 
hydroxide,  19 
in  dental  alloy,   determination   of, 

160 
nitrate,  185 

solutions,  430 
oxide,  19 

platinum  alloy,  19 
properties  of,  18 
reactions,  20 
recovery  of,  141 
solder  for,  133 
stains,  remov^al  of,  19 
thiosulphate,  19 
tin  alloys,  1 23 
titration  of  by  KCNS,  160 
by  XaCl,  160 
Silvering  mirror  (alloy  used),  40 
Simple  ethers,  211 

proteins,  272,  275,  278 
Skatol,  254 

Skatoxyl  potassium  sulphate,  254 
Small  calorie  (defined),  362 
Smaltite,  61 
Smelling  salts,  85 
Smithsonite,  64 
Smoky  urine,  328 
Soap,  267 
Soapilone,  74 
Sodium,  81 

acid  urate  (PI.  X,  Fig.  3),  355 
amalgams,  121 
bicarbonate,  82 
carbonate,  81 
chloride,  83,  185 

\  per  cent.  (PI.  VIII,  Fig.  2),  316 
decinormal  solulion,  159 
effect  on  metabolism,  364 
compounds,  81 
hydroxide,  81 

decinormal,  150 
nitrate,  83 
o.xalate  in  urine,  356 

microchemical  crs'stals,  171 
(PI.  II,  Fig.  4),  i"70 
perborate,  180,  185 

test  for  H2O2  (Exp.  20),  372 
peroxide,  81,  180,  185 


Sodium,  phosphates,  83 
and  uric  acid,  242 

potassium  tartrate,  84 

pyroantimonate,  84 

reaction  of,  84 

stannate,  41 
Sodium  stannite  preparation,  31,  41 

tetraborate,  176 

thiosulphate  N/io  solution,  155 

uranyl  acetate,  84 

urate,  in  urine,  355 

microchemical  crystals,  171 
_  (PI.  X,  Fig.  3),  355 

zincate,  65 
Soft  solder,  129,  130 
Solder,  129 

for  aluminium,  130,  131 

for  brass,  131 

for  gold,  131 

for  platinum,  133 

for  silver,  133 
Soldering  acid,  130 
Solids  in  saliva,  315 
Solid  solution,  117 
Solubility  tables,  91,  92 
Soluble  anhydrite,  72 

cotton,  264 
Solution  explained,  9 
Solvate  theory,  H.  C.  Jones,  9 
Solvay  process,  82 
Somnoform,  185 
Spathic  iron  ore,  53 
Specific  gravit}',  13 

of  amalgams,  127 

of  saliva,  292 

determination  of,  308 
Spence,  Dr.  S.  J.,  expansion  of  plaster, 

Ref.,  73 
Spermatozoa,  358 

(PI.  IX,  Fig.  2),  353 
Sperrylite,  45 
Spirit  of  Mindererus,  86 
Sputum,  297 
Standard  alloy,  125 

dental  alloy,  125 

solutions,  143 
Stannous  chloride,  41 
Stannum,  40 
Starch,  262 

experiments  with,  402 

hydrolysis  of  (Exp.  245),  416 

hydrolytic  products  of,  263 

paste  (E.xp.  178),  402 

preparation  (Exp.  177),  402 
Steapsin,  322 


INDEX 


453 


Stearic  acid,  217,  219 

digestion  of,  363 
Stearoptcn,  265 
Steel,  53 

carbon  in,  53 
Sterco-isomerism,  224 
Sterling  silver,  19,  115 
Stibium,  38 
Stibnite,  38 

Stiles,  Dr.  Percy  G.,  Ref.,  on  metab- 
olism, 363 
Stoke's  reagent,  note,  413 
Stomach  steapsin,  320 
Stovaine,  186 

and  PtiCU  (microchemical  test),  172 
(PI.  IV,  Fig.  4),  172 
Straight  chain  hydrocarbons,  198 
Stroma  of  blood  corpuscles,  287 
Strontium,  71 

o.xalate  (m.  c),  171 
(PI.  II,  Fig.  3),  170 

reactions  of,  71 

salts  and  flame  test,  71 
Strontianite,  71 
Sturine,  274 

Substituted  ammonias,  233 
Substitution  products  of  the  hydrocar- 
bons, 196 
Succinic  acid,  221 

natural  sources  of,  221 
Succinimide,  234 
Sucrose,  262 
Sugar  in  saliva,  300 

in  urine,  346 

of  lead,  23 

quantitative        determination        by 
Fehling's  solution,  347 

quantitative    determination   by   fer- 
mentation, 349 
Sugars,  259 

tests  for  (Exp.  167,  etc.),  400 
Sulphanilic  acid,  252 
Sulphates,  95,  98 

in  urine,  340 
Sidphides,  determination  of,  93,  95,  97 
Sulphites,  test  for,  94 
Sulphocyanates  in  saliva,  301,  302,  308 

test  for,  96 
Sulphocj'anic  acid,  230 
Sulphonol,  23 J 
Sidphones,  231 
Sulphonic  acids,  232 
Sulphur  compounds  (organic),  231 

tests  for,  195 

total  in  urine,  determination,  340 


Sulphuret  of  potassium,  80 

Sulphuric  acid,  dilute,  430 

Sulphuric  ether,  212 

Sulphur  iodides  (for  blow  pipe  test),  107 

Suprarenal  glands,  186 

Suprarenalin,  174 

Sweet  spirits  of  niter,  214 

Sylvanite,  42 

Sylvite,  78 

Symbols  (defined),  3 

Symmetrical  hydrocarbons,  246 

Syntonin,  276,  285 


Talcum,  74 
Tannic  acid,  186,  251 
Tannin,  186 
Tartar,  189 

composition  of,  190 

crude,  80 

emetic,  39,  225 
Tartaric  acid,  224 
Taurine,  232 

Taurocholic  acid  in  bile,  323 
Teeth,  analysis  of,  191 
Teeth  and  tartar,  189 
Teichmann's  hemin  crystals,  289 

(PI.  VII,  Fig.  2),  287 

test  (Exp.  239),  414 
Temporary  alloy,  125 
Terpenes,  267 
Tertiary  alcohols,  206 
Thein,  241 
Thermometers,  12 
Thioalcohol,  231 

Thiocyanate  in  saliva,  determination, 
308 

test  for,  96 
Thiocyanic  acid,  230 
Thioethers,  231 
Thioketones,  231 
Thiosulphates,  test  for,  94,  97 
Thorner,  on  acidity  of  rnilk,  Ref.,  282 
Thrombase,  286 
Thrombin,  286 
Thymol,  186,  247 

iodide,  186 
Thymophen,  187 
Thyroids,  187 
Tin,  40 

alloys,  40 

amalgams,  123 

cement,  138 

chloride,  preparation  of,  41 

reaction  with  HgCl2,  29 


454 


INDEX 


Tin,  compounds  of,  40 

gravimetric  determination  of,  163 

nitric  acid,  reaction  with,  41 
reactions  of,  41 
Tincture  of  iodine  for  reagent,  430 
Tinstone,  40 
Titration  (defined),  150 
ToUen's  reagent  (Exp.  85),  386 

preparation,  430 

test  for  aldehyde  (Exp.  85),  386 
Toluene,  245 
Toluol,  245 
Tribrom-methane,  203 
Tribrom-phenol,  184 

(M.  C),  171;  also  (Exp.  143),  396 

(PI.  Ill,  Fig.  5),  171 
Trichloracetic  acid,  187 
Trichloraldehyde,  208 
Trichlormcthane,  176,  203 
Tricresol,  248 
Trihydroxybenzene,  247 
Tri-iodomethane,  204 
Trimethylamine,  233,  234 
Trimethylbenzene,  246 
Trinitro  cellulose,  264 

phenol,  249 

preparation  (Exp.  147),  397 
Triolein,  266 
Trioxymethylene,  208 
Trioxypurin,  240 
Tripalmitin,  266 
Triple-bonded  hydrocarbons,  202 

phosphates,  355 
Tristearin,  266 
Tritenyl,  215 
Tropa-cocaine,  187 
TropoeoHn  (Exp.  255d),  420 

solution,  430 
Truedentalloy,  125 
Trypsin,  321 
Trypsinogen,  321 
Twentieth  Century  alloy,  125 
Type  metal,  115 
Tyrosin,  227,  251 

preparation,  434 

(PI.  V,  Fig.  6),  204 

U. 
Uffelmann's  reagent  (Exp.  257),  420 

preparation  of,  430 
Ultimate  analysis,  194 
Unsaturated  hydrocarbons,  201 
Unsymmetrical  hydrocarbons  (defined), 

246 
Uraninite,  70 


Uranium,  standard  solution  of,  339 
Uranyl  sodium  acetate,  84 
Urates  in  urine,  355 
Urea,  237,  238 

and  NaBrO  (reactions),  238 

and  H2O  (reactions),  237 
Urea  determined  by  Doremus  Hinds 
apparatus,  2,2,2, 

by  Ferris'  apparatus  (saliva),  311 

by  Squibb's  apparatus,  332 

determination  of,  311 

experiments  with,  394 

in  saliva,  300 

nitrate,  238 

(PI.  V,  Fig.  3),  204 

oxalate,  238 
(M.  C),  171 
(PI.  II,  Fig.  5),  170 

qualitative  test  for,  331 
Urea  (synthesis  of  Exp.  126),  393,  434 
Ureas,  substituted,  239 
Urease,  258 
Ureides  (defined),  239 
Uric  acid,  210,  241,  334 

(PL  X,  Fig.  I  and  2),  355 

and  lithium  salts,  242 

and  Na2HP04,  242 

determination,  334 
Cook's  method,  334 
Fohn's  method,  335 
Hopkin's  method,  335 

murexide  test  for,  394 

proportion  to  urea,  355 

in  urinary  sediments,  354 
Urinary  sediments,  353 
Urine,  326 
Urine,  abnormal  constituents,  343 

acetone  in,  350 

acidity  of,  329 

albumin  in,  343 

alkaline  phosphates  in,  337 

ammonia  in,  335 

analysis  blank  and  use,  359 

appearance  of,  328 

bile  in,  351 

brick  dust  deposit  in,  241 

causes  of  cloudy,  328 

chlorine  in,  337 

color  of,  327 

coloring  matter  in,  341 

epithelium  in,  356 

indoxyl  in,  341 

method  of  collecting,  327 

normal  solids  in,  331 

phosphates  in,  337 


INDEX 


455 


Urine,  estimation  of,  338.  339 

physical  properties  of,  327 

quantity,  327 

reaction,  329 

soluble  salts  in,  341 

specific  gravity,  329 

sulphates,  340 
Urinometer,  329 
UrobiUn,  341 
Urochrome,  341 
Uroerythrin,  341 
Urorosein,  341 


Valence  (defined),  3 
Valeric  acid,  218 
Vaseline,  200 
\'egetable  globulin,  434 
Vegetables,  oxalic  acid  in,  221 
Verdigris,  27 
Vinegar,  217 

determination  of  strength,  151 
test  for  malic  acid  (Exp.  113),  391 
Viscosity  of  saliva,  305 
Vitamines,  366 
Vitellin,  274 
Volatile  alkali,  87 

oils,  267 
Volumetric  analysis,  143 
V6n  Eckart's  alloy,  19 

W. 

Washing  soda,  81 

Water,  detection  of  in  alcohol  (Exp.  75), 

384 
Weights  and  measures.  11 
Weldon's  process  for  chlorine,  63 
WTieat  starch  (PI.  VI,  Fig.  4),  262 
White  arsenic,  32 

blood  corpuscles,  287 

copper  cement,  138 

lead.  2;^, 

precipitate,  28,  29 

\-itriol,  65 
Will  &  Varrentrap's  test  for  nitrogen, 

195 
Wilson,  Dr.  G.  H.,  expansion  of  plaster, 

Ref.,  72 
Witherite^  70 

Wohler's  test  lor  nitrogen,  195 
Wood's  metal,  12S 


Wood  spirit,  206 
Wool  fibers  (PI.  IX,  Fig.  6)-,  353 
Wrought  iron,  53 
carbon  in,  53 

X. 

Xanthin,  240 

Xanthroproteic  test  (E.xp.  187),  40S 

Xylene,  245 

Xylol,  245 

Xylose,  259 


Yeast,  256 

ceUs  and  molds  (PI.  X,  Fig.  4),  355 
Yellow  prussiate  of  potassium,  229 
Yellow  wash,  28 


Zein,  277 
Zinc,  64 
Zincates,  65,  66 
Zinc  alloys,  65 

amalgams,  123 

blende,  64 

carbonate,  64,  65 

compounds,  65 

ferrocyanide,  66 

gold  solder,  131 

gra\imetric  determination  of,  165 

hydrate,  65 

in  amalgam  aUoys,  65 

in  dental  alloys,  124 

lactate,  224 

melting  point,  64 

oxalate,  66 

(PI.  II,  Fig.  6),  170 

oxide,  preparation  of,  136    - 

oxj'chloride,  137 

oxj^hosphate,  135 

oxysulphate,  137 

pero.^de,  180 

properties  of,  64 

reactions  of,  65 

sarcolactate,  223 

separation  from  manganese,  67 

sulphate,  65 

sulphide,  65 

volumetric  determination  of,  162 

white,  65 
Zymase,  258 
Zjonogens,  257 


S 


nrt  «5 


e. 


COLUMBIA  UNIVERSITY  LIBRARIES  (hsi.stx) 

RK  290  Sm5  1917  C.1 

Lecture-notes  on  cMp'-'  ■  "  ,  '■"  "••■':■  st 


2002354659 


TABLE  OF  ATOMIC   WEIGHTS   (1917) 


Aluminium 

Al 

27.1 

Molybdenum 

.Mo 

96.0 

Antimony 

Sb 

120.2 

Neodymium 

.Nd 

144.3 

Argon 

A 

39.88 

Neon 

.Ne 

20.2 

Arsenic : 

As 

74.96 

Nickel 

.Ni 

58.68 

Barium 

Ba 

137.37 

Niton  (radium  emanation) 

.Nt 

222.4 

Bismuth 

Bi 

208.0 

Nitrogen 

.N 

14.01 

Boron 

B 

11.0 

Osmium 

.Os 

190.9 

Bromine 

Br 

79.92 

Oxygen 

.0 

16.00 

Cadmium 

Cd 

112.40 

Palladium 

.Pd 

106.7 

Caesium 

Cs 

132.81 

Phosphorus 

P 

31.04 

Calcimn 

Ca 

40.07 

Platimmi 

.Pt 

195.2 

Carbon 

C 

12.005 

Potassium 

.K 

39.10 

Cerium 

Ce 

140.25 

Praseodymiima 

Pr 

140.9 

Chlorine 

CI 

35.46 

Radium 

.Ra 

226.0 

Chromium 

Cr 

52.0 

Rhodimn 

.Rh 

102.9 

Cobalt 

Co 

58.97 

Rubidium 

.Rb 

85.45 

Columbium 

Cb 

93.1 

Ruthenium 

.Ru 

101.7 

Copper 

Cu 

63.57 

Samarium 

.Sa 

150.4 

Dysprosium 

Dy 

162.5 

Scandium 

.Sc 

44.1 

Erbium 

Er 

167.7 

Selenium 

.Se 

79.2 

Europium 

Eu 

152.0 

SiUcon 

.Si 

28.3 

Fluorine 

F 

19.0 

Silver 

-Ag 

107.88 

Gadolinium 

Gd 

157.3 

Sodium 

.Na 

23.00 

GaUium 

Ga 

69.9 

Strontium 

.Sr 

87.63 

Germanimn 

Ge 

72.5 

Sulfur 

.S 

32.06 

Glucinium 

Gl 

9.1 

Tantalum 

.Ta 

181.5 

Gold 

Au 

197.2 

Tellurium 

.Te 

127.5 

Heliima 

He 

4.00 

Terbium 

.Tb 

159.2 

Holmivun 

Ho 

163.5 

ThaUium - 

.Tl 

204.0 

Hydrogen 

H 

1.008 

Thorium 

.Th 

232.4 

Indium 

In 

114.8 

Thuhum 

.Tm 

168.5 

Iodine 

I 

126.92 

Tin 

.Sn 

118.7 

Iridium 

Ir 

193.1 

Titanium 

.Ti 

48.1 

Iron 

Fe 

55.84 

Tungsten. 

.W 

184.0 

Krypton 

Kr 

82.92 

Uranium 

.U 

238.2 

Lanthanum 

La 

139.0 

Vanadium 

.V 

51.0 

Lead 

Pb 

207.20 

Xenon 

.Xe 

130.2 

Lithium 

Li 

6.94 

Ytterbium  (Neoytterbium) 

.11) 

173.5 

Lutecium 

Lu 

175.0 

Yttrium 

.Yt 

88.7 

Magnesium 

Mg 

24.32 

Zinc 

.Zn 

65.37 

Manganese 

Mn 

54.93 

Zirconium 

.Zr 

90.6 

Mercury 

Hg 

200.6 

